Wow. I know nothing about bikes but I downloaded this fixed gear documentary the other day after hearing many people talk about how nutty it was. It was pretty interesting. I'd love to sit here and make jokes about their silly tight pants, but I think you really have to have a death wish to fly down a San Francisco hill and barrel through an active intersection without any brakes. Strangely enough, the trailer doesn't even show most of the really crazy shit in it.
Yeah those fixed gear guys are just a different breed altogether. And realize it's not just no brakes - if the wheels are turning, so is the crank. So they have to pedal down the hill, with no brakes, in traffic. On tires that are probably an inch or less wide. The fact that they don't wear helmets is completely nuts.

I'll stick with my mountain bike with disc brakes, giant tires and suspension.