SF's largest pure-dance event (formerly "Lovefest") spices up the early fall and has been a hit since it's inaugural run in 2004. An offshoot of the Berlin based Love Parade, the event starts with a dance downtown parade (with dancing beforehand), and follows up with a dance party outside City Hall.
Check out the photos and dress to thrill, or kill... and groove yourself into a state of bliss. For any of many after-parties around town - keep ears open, nose sniffing, and feet moving :)
Owing to some local issues and the recent tragedy in Germany, the daytime event has been cancelled for 2010 - the night events are still on.
Website: http://www.sflovevolution.org
Wikipedia: http://en.wikipedia.org/wiki/Lovefest