I'll pretty much echo what others have said... we got to where we are to start with because of our habits... to change our habits must change... about 5 years ago I'd lost about 45lbs (and still had about 60-70 to loose ideally)... about 20 of that in the course of under 2 months by being very strict about diet and busting my behind in the gym... then I moved, lost my weight machine and compromised my diet badly... it took about 4 years before I gained it all back.
this last may I simply started eating a little better and drinking a lot more water... toss in about 10hrs of riding a month and i'm down about 25lbs now... with the cold weather I'm going to join a gym, In the past I've found weight loss really likes it when I build up some muscle (wife likes it also ;-)
in short... I think it's pretty common for us big folks... its easy to slip back up... if you stop exercising you have to cut out food and I think that tends to be the big issue for most of us... we like to eat... at thanksgiving I've got to walk away from the table before I feel full... so easy to just keep picking at the food even if i'm full :-/