The local fixie couriers near where I work always make me laugh :roll:
They think they're fast, but they're not. I can out accelerate them by using a lower gear. I can go faster because I've got a higher gear. I can go faster round corners because I can lift the inner pedal up. And as I can stop quicker than a car, I'm in a better and 'safer' position to take risks, should I need to get through something quickly. Not all couriers are this daft though - the only ones I know all use cyclocross or mountain bikes.
And I do know all about fixed wheel bikes. I've been racing at the velodrome for years and have a lovely track bike that's never been on the road, and never will go on the road. It's where it belongs, and not at risk of running any pedestrians over !
That embarrasing but funny MC Spandex video summed it up quite well...
Rant over !