I second the recommendation that everybody read John Pucher's work (he has posted most of his articles on his website:
http://policy.rutgers.edu/faculty/pucher/ ).
As for me, I started commuting by bike when I realized it was faster and easier than commuting by car. Dense cities with limited parking encourage bikes (as well as walking and transit). If you want to get more people on bikes, impose an urban sprawl limit and increase parking fees.
Outside of dense urban centers, it can be difficult to bike because the car traffic moves too fast; in those environments, separate bike paths can be good -- but not many people will use them until you make it slower and more of a hassle to use a car.