I was planning on running singlespeed for a while; therefore, brakes. I live atop a mile of 6% grade, so the first mile of every ride I do is pretty fast (the last mile is kind of slow...). "Forgetting" to pedal half-way down that would get me killed. The only bike-related thing I've ever been on that doesn't allow coasting is a spin bike at the gym. Learning to always pedal at 40mph probably isn't the best idea.