For the latest in ghost bikes in San Francisco read the blog I Love Biking SF & OAK.
Jo Slota began Ghost Bike in San Francisco as a way to mark the passing of bicycles. Since 2002, he identified 23 bikes, that had been abandoned and stripped of their parts, painted them white and photographed them. These bikes are mapped and can be viewed here.
Jo is still working with ghost bikes, helping to install them for cyclists that are killed in San Francisco.
While his project may not have been designed to memorialize fallen cyclists, the project inspired Ghost Bike Pittsburgh in 2004 to paint their bicycles white. The inspiration to install bicycles as memorials comes from St. Louis, but St. Louis' earlier memorials in 2003 were not originally painted white. For a more detailed account go here