I've lost about 20-23lbs since I've started commuting 6 months ago. Went from 190lbs to 167/170lbs, depending on the day. The first 10lbs dropped in the first month, and then I level off for a bit, then lost the rest more gradually. My commute is about 30mile round trip. I don't really watch what I eat at all though and still drink plenty of beer.