Having a front brake is very important... it's against the law not to have one most places, and frankly I think anyone who rides without one is an idiot. You can slow down with your feet very effectively in most circumstances, but for steep descents and sudden panic stops a brake is crucial.

The cool kids may not have brakes on their fixies, but then again I don't see too many of them over 30, so either they're getting killed or they're wising up I personally had both front and rear brakes on the fixie I owned most recently. It was a ton of fun to ride. And I didn't use the brakes much, but when I did need 'em I was glad they were there.