My favorite thing about getting around by bicycle, besides just getting to ride a bicycle everywhere, is that I can eat whatever I want, pretty much, and never need to worry about gaining weight. Dinner at a pub with two or three beers is really not an issue.

If you stop commuting during the winter you'll want to supplement your riding with something else, but if you live somewhere that doesn't have much snow or ice you can pretty much ride all year round.

It also helps if you push yourself when commuting (when it's safe, of course) so that you're right at your aerobic limit most of the ride to and from work. That way you don't just get some exercise everyday, you get some really good, intense exercise.