In "Is it possible to live in America without a car?", author Bill Gifford tells an inspiring story of his efforts to give up using his car in favor of bicycling everywhere.
I've tried bicycling as a means of transportation just for fun on occasions. It's tremendous exercise and does save money. However, in the larger metro areas of the US, bicycling can be dangerous due to uncivilized, pickup-driving meanies who get offended when a fitness-conscious person wants to share the road with them. That's why I contribute to a program called "Share the Road".
I hope the situation is better outside of the US.