SEC Form 4

FORM 4		UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940	OMB APPROVAL OMB Number: 3235-0287 Estimated average burden hours per response: 0.5
	Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

1. Name and Address of Reporting Person* MADRONA VENTURE FUND I-A L P (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip)	2. Issuer Name and Ticker or Trading Symbol Isilon Systems, Inc. [ ISLN ]	5. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)
	3. Date of Earliest Transaction (Month/Day/Year) 12/20/2006
	4. If Amendment, Date of Original Filed (Month/Day/Year)	6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock	12/20/2006		C(1)		2,990,473	A	(2)	2,990,473	I	See footnote(3)
Common Stock	12/20/2006		C(1)		2,697,184	A	(2)	5,687,657	I	See footnote(4)
Common Stock	12/20/2006		C(1)		2,352,684	A	(2)	8,040,341	I	See footnote(5)
Common Stock	12/20/2006		C(1)		1,670,154	A	(2)	9,710,495	I	See footnote(6)
Common Stock	12/20/2006		C(1)		298,643	A	(2)	10,009,138	I	See footnote(7)

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Series A Preferred Stock	(2)	12/20/2006		C			2,990,473	(8)	(8)	Common Stock	2,990,473	$0.00	0	I	See footnote(3)
Series B Preferred Stock	(2)	12/20/2006		C			2,697,184	(8)	(8)	Common Stock	2,697,184	$0.00	0	I	See footnote(4)
Series C Preferred Stock	(2)	12/20/2006		C			2,352,684	(8)	(8)	Common Stock	2,352,684	$0.00	0	I	See footnote(5)
Series D Preferred Stock	(2)	12/20/2006		C			1,670,154	(8)	(8)	Common Stock	1,670,154	$0.00	0	I	See footnote(6)
Series E Preferred Stock	(2)	12/20/2006		C			298,643	(8)	(8)	Common Stock	298,643	$0.00	0	I	See footnote(7)

1. Name and Address of Reporting Person* MADRONA VENTURE FUND I-A L P (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* Madrona Investment Partners, LLC (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* MADRONA MANAGING DIRECTOR FUND, LLC (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

1. Name and Address of Reporting Person* MADRONA VENTURE FUND I-B, LP (Last) (First) (Middle) 1000 SECOND AVENUE SUITE 3700 (Street) SEATTLE WA 98104 (City) (State) (Zip) Relationship of Reporting Person(s) to Issuer Director X 10% Owner Officer (give title below) Other (specify below)

Explanation of Responses:

1. Represents shares of Common Stock issued upon the conversion of shares of Preferred Stock on a 1-for-1 basis.

2. Not applicable.

3. Includes 2,411,195 shares held by Madrona Venture Fund I-A, LP ("Madrona Venture Fund A"), 262,430 shares held by Madrona Venture Fund I-B, LP ("Madrona Venture Fund B") and 316,848 shares held by Madrona Managing Director Fund LLC ("Madrona Managing Director Fund"). Matthew McIlwain (who is a director of the Issuer and files separate Section 16(a) reports) is a managing director of various entities affiliated with Madrona. Madrona Investment Partners, LLC is the general partner of Madrona Venture Fund A and Madrona Venture Fund B. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

4. Includes 2,174,726 shares held by Madrona Venture Fund A, 236,688 shares held by Madrona Venture Fund B and 285,770 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

5. Includes 1,896,958 shares held by Madrona Venture Fund A, 206,456 shares held by Madrona Venture Fund B and 249,270 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

6. Includes 1,346,637 shares held by Madrona Venture Fund A, 146,562 shares held by Madrona Venture Fund B and 176,955 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

7. Includes 240,795 shares held by Madrona Venture Fund A, 26,207 shares held by Madrona Venture Fund B and 31,641 shares held by Madrona Managing Director Fund. Each of the Filing Persons disclaims beneficial ownership of the shares except to the extent of his or its pecuniary interest therein.

8. Each share of Preferred Stock converted into one share of Common Stock on December 20, 2006 and has no expiration date.

Remarks:

	/s/ Matthew S. McIlwain	12/20/2006
	Matthew S. McIlwain	12/20/2006
	Matthew S. McIlwain	12/20/2006
	Matthew S. McIlwain	12/20/2006
	** Signature of Reporting Person	Date
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