I've lived in San Francisco for two years and somehow I've always been out of town during Bay to Breakers. This year, a friend came to visit me that weekend, so I finally got to see the spectacle.
Frankly, it is sort of like every other event in San Francisco. Several naked people (I worked very hard to keep them out of my photos), others dressed in crazy costumes, a lot of drinking (even though there was an "absolutely no tolerance" policy this year) and a rather strong smell of various organic materials in the air.
Although some of the costumes were rather incredible...
Salmon swimming up stream (they start at the end and run in the wrong direction):
And my favorite shot: