For health reasons and for savings. When we moved to Juneau and were shopping for a house, I didn't want a place too close to work, I wanted a decent bike ride between home and work. The 6.9 mile distance seems to offer a good balance in time in commute and getting a decent workout. I don't worry much about not getting exercise because it's baked into my daily routine.

On the saving money side. I find that the savings in terms of gas is actually fairly minimal. When I was riding my mountain bike, I was surprised how small the savings was in terms of gas. 2400 miles per year, divide by 20 miles per gallon = 120 gallons saved times $4 something per gallon, say $500 per year. OTOH, I was spending a fair amount on maintenence on my bike, about $200 a year. So what a net saving of $300 per year...

EXCEPT

I don't own a second car. If I were commuting by car, I'd own another car. We have one car, my wife drives that. I rarely if every have the option of driving a car to work. So if you figure not owning a (second) car for 20 plus years the savings easily rise into the tens of thousands.