There's an interesting article in the LA Times this week with research explaining how our body functions regarding weight loss and why it's so difficult to maintain.
There are good suggestions however describing how people have kept it off.
If you go to the LATimes website, click on the health section (left hand side) and scroll down, you'll find the article (there's others about fat cells and weight loss as well.)
It helped me understand my weight gain after losing over 60 lbs. on MF 2+ years ago. I plan on remembering and utilizing this information to maintain a thin, healthy body once I reach my goals!
Hope you find it helps!