You lose about a pound a week when you burn 500 cal per day more than you eat (1 pound=3500 cal). There is a rule of thumb that biking burns 40-50 cal/mile which is probably about twice the rate that I appear to burn at (based on estimating calories-out from observations of calories-in and weight loss). I have a ~7 mile each way commute, I didn't really wind up losing weight until I started adding in 12 mile lunchtime rides. That's mostly a reflection on what I was eating, I guess.

Others have mentioned that regardless of weight loss there is shape change.