I was a courier in boston for a few months: excellent city to ride in. I live in chicago now which is still a great biking city, but overall, not as good. The streets here are wider, the cars are bigger, and the traffic is faster. Being on a bike in boston rules because your advantage over cars is so extreme that you can fly around the city while laughing at the poor suckers stuck in traffic. In chicago you have to be more careful about not becoming roadkill.