<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>0212 - Disclosure - Income Taxes</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2010 - 12/31/2010
USD ($)

USD ($) / shares
</KeyName><CurrencySymbol>$</CurrencySymbol><contextRef><ContextID>Jan-01-2010_Dec-31-2010</ContextID><EntitySchema>http://www.sec.gov/CIK</EntitySchema><EntityValue>0001107332</EntityValue><PeriodDisplayName /><PeriodType>duration</PeriodType><PeriodStartDate>2010-01-01T00:00:00</PeriodStartDate><PeriodEndDate>2010-12-31T00:00:00</PeriodEndDate><Segments /><Scenarios /></contextRef><UPS><UnitProperty><UnitID>USD</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>Shares</UnitID><UnitType>Standard</UnitType><StandardMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></StandardMeasure><Scale>0</Scale></UnitProperty><UnitProperty><UnitID>USDEPS</UnitID><UnitType>Divide</UnitType><NumeratorMeasure><MeasureSchema>http://www.xbrl.org/2003/iso4217</MeasureSchema><MeasureValue>USD</MeasureValue><MeasureNamespace>iso4217</MeasureNamespace></NumeratorMeasure><DenominatorMeasure><MeasureSchema>http://www.xbrl.org/2003/instance</MeasureSchema><MeasureValue>shares</MeasureValue><MeasureNamespace>xbrli</MeasureNamespace></DenominatorMeasure><Scale>0</Scale></UnitProperty></UPS><CurrencyCode>USD</CurrencyCode><OriginalCurrencyCode>USD</OriginalCurrencyCode></MCU><CurrencySymbol>$</CurrencySymbol><Labels><Label Id="1" Label="12 Months Ended" /><Label Id="2" Label="Dec. 31, 2010" /></Labels></Column></Columns><Rows><Row><Id>2</Id><IsAbstractGroupTitle>true</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_IncomeTaxExpenseBenefitAbstract</ElementName><ElementPrefix>us-gaap</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>No definition available.</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole /><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText /><NonNumericTextHeader /><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>xbrli:stringItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>No definition available.</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Income Taxes [Abstract]</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_IncomeTaxDisclosureTextBlock</ElementName><ElementPrefix>us-gaap</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>No definition available.</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>verboselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;!--DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd" --&gt;
   &lt;!-- Begin Block Tagged Note 12 - us-gaap:IncomeTaxDisclosureTextBlock--&gt;
   &lt;div style="margin-left: 0%"&gt;
   &lt;div style="margin-top: 12pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;table width="100%" border="0" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: transparent; text-align: left"&gt;
   &lt;tr&gt;
       &lt;td width="5%"&gt;&lt;/td&gt;
       &lt;td width="95%"&gt;&lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="top"&gt;
       &lt;td&gt;
       &lt;b&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;12.&amp;#160;&amp;#160;&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
       &lt;td&gt;
       &lt;b&gt;&lt;font style="font-family: 'Times New Roman', Times"&gt;INCOME
       TAXES&lt;/font&gt;&lt;/b&gt;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;/table&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       We recognized $0.4&amp;#160;million in income tax benefit in 2010
       relating to refundable credits, compared with no income tax
       expense or benefit in 2009 or 2008.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       As of December&amp;#160;31, 2010, we had federal and state net
       operating loss carryforwards (&amp;#8220;NOLs&amp;#8221;) of approximately
       $843&amp;#160;million and $252&amp;#160;million, respectively. We also
       had federal and state research and development credit
       carryforwards (&amp;#8220;R&amp;#038;D Credits&amp;#8221;) of approximately
       $20.7&amp;#160;million and $2.6&amp;#160;million, respectively. The NOLs
       and R&amp;#038;D Credits will expire at various dates, beginning in
       2011 through 2030, if not utilized.
   &lt;/div&gt;
   &lt;!-- XBRL Pagebreak Begin --&gt;
   &lt;/div&gt;
   &lt;!-- END PAGE WIDTH --&gt;
   &lt;!-- PAGEBREAK --&gt;
   &lt;div style="margin-left: 0%"&gt;
   &lt;!-- BEGIN PAGE WIDTH --&gt;
   &lt;div align="center" style="margin-left: 0%; margin-right: 0%; font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: transparent"&gt;
   &lt;b&gt;
   &lt;font style="font-family: 'Times New Roman', Times"&gt;
   &lt;/font&gt;
   &lt;/b&gt;
   &lt;/div&gt;
   &lt;div style="margin-top: 0pt; font-size: 1pt"&gt;
   &lt;/div&gt;
   &lt;div align="center" style="margin-left: 0%; margin-right: 0%; font-size: 10pt; font-family: Arial, Helvetica; color: #000000; background: transparent"&gt;
   &lt;b&gt;
   &lt;font style="font-family: 'Times New Roman', Times"&gt;
   &lt;/font&gt;
   &lt;/b&gt;
   &lt;/div&gt;
   &lt;!-- XBRL Pagebreak End --&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       We are subject to U.S.&amp;#160;federal and state income tax
       examinations for years after 2005 and 2004, respectively.
       However, carryforward attributes that were generated prior to
       2004&amp;#160;may still be adjusted by a taxing authority upon
       examination if the attributes have been or will be used in a
       future period.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       We recognize interest and penalties accrued on any unrecognized
       tax benefits as a component of income tax expense. During the
       year ended December&amp;#160;31, 2010, 2009 and 2008, we did not
       have any accrued interest or penalties associated with any
       unrecognized tax benefits.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       Deferred income taxes reflect the net tax effects of temporary
       differences between the carrying amounts of assets and
       liabilities for financial reporting purposes and the amounts
       used for income tax purposes. Significant components of our
       deferred tax assets were as follows:
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;table border="0" width="100%" align="center" cellpadding="0" cellspacing="0" style="font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent; text-align: left"&gt;
   &lt;!-- Table Width Row BEGIN --&gt;
   &lt;tr style="font-size: 1pt" valign="bottom"&gt;
       &lt;td width="77%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=01 type=maindata --&gt;
       &lt;td width="2%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=gutter --&gt;
       &lt;td width="1%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=lead --&gt;
       &lt;td width="7%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=body --&gt;
       &lt;td width="1%" align="left"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=02 type=hang1 --&gt;
       &lt;td width="3%"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=gutter --&gt;
       &lt;td width="1%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=lead --&gt;
       &lt;td width="7%" align="right"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=body --&gt;
       &lt;td width="1%" align="left"&gt;&amp;#160;&lt;/td&gt;&lt;!-- colindex=03 type=hang1 --&gt;
   &lt;/tr&gt;
   &lt;!-- Table Width Row END --&gt;
   &lt;!-- TableOutputHead --&gt;
   &lt;tr style="font-size: 8pt" valign="bottom" align="center"&gt;
   &lt;td nowrap="nowrap" align="center" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="6" align="center" valign="bottom" style="border-bottom: 1px solid #000000"&gt;
       &lt;b&gt;December&amp;#160;31,&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom" align="center"&gt;
   &lt;td nowrap="nowrap" align="center" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #000000"&gt;
       &lt;b&gt;2010&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="2" nowrap="nowrap" align="center" valign="bottom" style="border-bottom: 1px solid #000000"&gt;
       &lt;b&gt;2009&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="font-size: 8pt" valign="bottom" align="center"&gt;
   &lt;td nowrap="nowrap" align="center" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td colspan="6" align="center" valign="bottom"&gt;
       &lt;b&gt;(In thousands)&lt;/b&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr style="line-height: 3pt; font-size: 1pt"&gt;
   &lt;td&gt;&amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;!-- TableOutputBody --&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Deferred tax assets:
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Net operating loss carryforwards
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       309,096
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       213,157
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Research credits
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       23,331
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       18,379
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Stock-based compensation
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       11,411
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       4,610
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Other
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       9,728
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       4,497
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="font-size: 1pt"&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Total deferred tax assets
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       353,566
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       240,643
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="background: #cceeff"&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Valuation allowance
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       (353,566
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       )
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       (240,643
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       )
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="font-size: 1pt"&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 1px solid #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom"&gt;
   &lt;td align="left" valign="bottom"&gt;
   &lt;div style="text-indent: -10pt; margin-left: 10pt"&gt;
       Net deferred tax assets and liabilities
   &lt;/div&gt;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       &amp;#8212;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
       $
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="right" valign="bottom"&gt;
       &amp;#8212;
   &lt;/td&gt;
   &lt;td nowrap="nowrap" align="left" valign="bottom"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;tr valign="bottom" style="font-size: 1pt"&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td style="border-top: 3px double #000000"&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;td&gt;
   &amp;#160;
   &lt;/td&gt;
   &lt;/tr&gt;
   &lt;/table&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 0%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       The net deferred tax asset has been fully offset by a valuation
       allowance. The valuation allowance increased by
       $113&amp;#160;million, $29.2&amp;#160;million and $26.0&amp;#160;million
       during the years ended December&amp;#160;31, 2010, 2009 and 2008,
       respectively.
   &lt;/div&gt;
   &lt;div style="margin-top: 6pt; font-size: 1pt"&gt;&amp;#160;
   &lt;/div&gt;
   &lt;div align="left" style="margin-left: 0%; margin-right: 0%; text-indent: 4%; font-size: 10pt; font-family: 'Times New Roman', Times; color: #000000; background: transparent"&gt;
       Realization of deferred tax assets is dependent on future
       earnings, if any, the timing and amount of which are uncertain.
       Accordingly, the deferred tax assets have been offset by a
       valuation allowance. The valuation allowance relates primarily
       to net deferred tax assets from operating losses. Excess tax
       benefits associated with stock option exercises are recorded
       directly to stockholders&amp;#8217; equity only when realized. As a
       result, the excess tax benefits included in net operating loss
       carryforwards, but not reflected in deferred tax assets, for
       fiscal year 2010 and 2009 are $146.7&amp;#160;million and
       $46.2&amp;#160;million, respectively.
   &lt;/div&gt;
   &lt;/div&gt;
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 -Publisher SEC
 -Name Regulation S-X (SX)
 -Number 210
 -Section 08
 -Paragraph h
 -Article 4

Reference 2: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 109
 -Paragraph 136, 172

Reference 3: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 109
 -Paragraph 43, 44, 45, 46, 47, 48, 49

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