In 2000 I managed to lose 70 pounds, and haven't gained but more than 10 pounds (usually winter weight since).
I would only recommend dieting if you think you are in danger of having a serious medical condition. For instance my father has type 2 "diabetus" because he's at least 100 pounds over the typical weight for his height. Seeing that at the time I was only 5'5 (maybe) and 250 pounds myself I needed to do something about it.
Also it's nice to lose weight, but it's just too much work!