A friend of mine just (re)started cycling this past summer and bought a full suspension MTB (Mongoose Otero Super). He lost 22lbs in 4 months. He also got his brother into riding and rides China Camp State Park about twice a week with him after work.

I finally convinced him to buy a road(ish) bike, a cyclocross bike (Fuji Cross Comp) actually and have been taking him an a road rides at night. The next time he rode with his brother at China Camp on his MTB, his brother commented that he got faster.