I couldn't give up cars completely myself... But I have talked to a few guys that don't own one themselves. When I was in Boston, MA, I talked to a few guys that were car-less. One guy was a bike messenger that ran a fixed gear and was on it 40+ hours a week and just walked or took the train "T" to get where else he needed to go. Another was a guy that rode his fixed gear bike from Maine to Boston, went to school, then rode back home every summer. Never got a clear answer on the distance traveled in that trip though. It's quite do-able and I'd love to do so myself.... It just won't happen for me. I love driving too much.
How the heck did he get his clothes and stuff he needed home for the summer?