I agree that exercise definitely helps, especially in maintaining weight loss. But I read something interesting concerning which of the two, calorie reduction or exercise, is more important.
Overall, I think calorie reduction is key. What I read put it this way: it can take a couple hours of exercise to burn off a candy bar, whereas simply omitting eating it requires no further action on your part! Just not eating those extra calories is much simpler than trying to burn them off later (although having the will power not to eat the candy bar is easier said than done!)
Ann