I started with a 3-mile bike commute. Which I thought was great, no need to drive, save $, etc.
Recently I moved and now I have 12-mile bike commute, which I cruise easily on my road bike in the summer, and push through the ice and snow on my fat-tire bike in the winter. And who knew it would be so much better than that wussy 3-mile ride!? Its so great I've turned down free rides home to bicycle instead.
With 12 miles I always get a great workout before and after work. When people at work look/talk to me like i'm crazy I just tell them how badass it is being able to ride like that every day - the testosterone level in the room increases, and more work gets done that day! Being engineers we need a good testosterone pump-up.
Knowing that I can do more miles has increased my flexibility; when I move again I know that I can look for a place further than before!
The only good thing about the 3-mile commute was that I passed by a workout gym with big open windows in the front. I got the comic relief of people who had drove to a gym, got on an exercise bike, and would drive to work after. I wonder if knocking out the middle man ever occurred to them.