Dammit. I always get asked this so I'll copy and paste from bmx forum
"yeah i once thought "self. i wonder how much fun you can have with front brakes. but wait... i only have one set. i know how to solve that problem. only fronts" and i haven't looked back since. pros; they are alot of fun. weigh a teeny bit less than rear brakes (less brake cable) you get to use brakes without worrying about getting the cable twisted and without a heavy gyro ever looked at a super GT race bike? they have massive dual front disk brakes and only a little rear disk brake. similar with downhill mountain bikes. when you use brakes all your weight shifts to the front so you therefore get alot more brakeing power. cons; you have to tell all these things to everybody who asks "why do you only have front brakes?"