My commute is very short these days as I chose my home to be close to work and the amenities I use daily. In winter it helps as it gets pretty cold and snowy here, it can double commute times. It also affords me the opportunity to ride the excellent river valley bike paths for 2/3 of the way. Trees, the river, birds, the occasional deer, beaver and porcupine: a great way to start the day.
I'm 37 (in 2003) and have never owned a car. Yes, I have a good job, I choose not to spend my money on cars. I ride a winterized '94 Specialized Rockhopper (studded tires, lights, fenders and suspension stem) and in summer I rocket to work on a Specialized Allez road bike. I own a BOB trailer in which I've carried everything from rainbarrels, to 8 foot 2x4's, to bales of fibreglass insulation, to guitar amplifiers.
The two best days of commuting thus far: 1) The day I broke the 10 minute mark on my summer ride to work. I'm down to 8 minutes now. 2) The day I made the severly off-camber, right angle, downhill corner on my winter ride without dabbing. This snowy turn on an unshoveled sidewalk had defeated me for several years. After I made it I was cheering so hard I endoed into a snowbank further down the hill! I work in retail where success is nebulous and subjective, it's great to have concrete accomplishments as a part of my daily commute. There's also a great sense of achievement when arriving at work on your bike on a -38c day (only happened once) or on a day where it snow 15cm or more the night before (a couple of times a year).
Ride because it's good for you. Ride because it's good for the world. Ride because it's good for your bank account. Ride because it's good fun. Any one of these is enough, but all together....?