The City and County of San Francisco has a new open data site:
Please follow the link to the site to search, browse and view San Francisco data.

Description: A total of 74 AutoCAD drawings representing the cadastral fabric of the City; each drawing (.dwg) file corresponds to an area of the City defined by the Assessor Block numbers. For example, sf05.dwg is the cadastral drawing that covers Blocks 0500 through 0599. Also included is an updated feature drawing that includes curb lines for the City.
Updated on December 7, 2011.
Agency Name: Department of Public Works
Date Released: Dec 7, 2011
Time Period: Current
Frequency: As-needed
Location of dataset:
Format: .DWG
Location of Data Dictionary:

DataSF is a clearinghouse of datasets available from the City & County of San Francisco. Our goal in releasing this site is:
(1) improve access to data
(2) help our community create innovative apps
(3) understand what datasets you'd like to see
(4) get feedback on the quality of our datasets.