Eric Fischer has been having a good bit of fun with maps lately. In his latest, he animates movements of the San Francisco MUNI (that's their bus system) over the month of June 2010. Each second of in the video represents about an hour in real life.
As you might expect, traffic dwindles during the late/early hours from midnight to four in the morning. Then like clockwork, it picks up again. My knowledge of San Francisco geography has always sucked, so maybe a local can point out some of the interesting areas. If my orientation is correct though, that main street that runs from southwest to northeast and seems to stay lit through the night is Market.
This of course is reminiscent of Stamen's Cabspotting, but much more raw, without any trails or ghostly footprints.