It is a truth universally acknowledged that fixed-gear cyclists, zipping through traffic in open disdain of hand-brakes (and often, helmets), have a shorter lifespan than the general population--although it's still a point of heated debate as to whether that's caused by the incidence of massive head trauma or by sexual exhaustion.
Nevertheless, whether lifestyle statement or fashion pose, they're out there.
As I freely confessed to a fixie rider who was riding with me on the MAX from Goose Hollow up to the Zoo, I'm sure that as a group they have stones many times the size of my helmeted and rear-view mirrored self. I have an odd sort of respect for the cowboy ethos of the bike couriers. (Demonstrating that you can too stop a fixed gear bike on a dime--by jamming a stick between the wheel and the frame--was lunatic but somehow inspired just the same. And after all, no one said anything about stopping the rider on a dime too.)
Still, as Harry Esteve points out, fixed-gear enthusiasts still have one challenge looming on the horizon that even they may find difficult to handle: the possibility of a faint glimmer of unwanted respectability.
Not cool. The only thing worse would be an endorsement from Tipper Gore.