While on the subject of people in costume, be sure to check out Daniel Jarvis's slightly untimely video about this year's Halloween in SF.  It's packed full of fun stuff like a human jellyfish (above), a lightsaber duel on Divis, zombies making out, a Teletubby that wants to poison you, and a shark that looks like she's sexually attracted to a parking meter.  Check it:

Halloween SF 2010 from daniel jarvis on Vimeo.