I suppose there could be more than one Evan Williams in San Francisco, but 601 4th Street #3P certainly looks like the residence of one of Twitter's cofounders. Twitter was founded in 2006 and didn't begin to take off until 2007 but Evan Williams purchased #3P for $1.5 million in October 2006. Unfortunately for him, after almost 5 months asking $1.498M the price has been dropped to $1.398M.
I bet some tweeting has been done from here.
Hey, he probably doesn't need the money.... so why not try to snap it up for less?