As long as we're on this discussion, I'll share my story.
As many of you know, I'm quite slender, and both my parents' families are quite slender as well. We don't eat especially well, and we're not health nuts, but I guess you could just say it's good genes. From about 15 years of age to 23, I've been 5'6", 135-140 lbs. No matter what I'd do or eat, it wouldn't change. Now that I've moved out though, I've gained about 10 lbs. It went right up from 137-145 and stayed there, but now I'm getting close to 150 and staying there consistently. This isn't where I want to be at all, and all the weight is going to my gut, nowhere else. I eat out too much with my friends. It seems like whenever I meet with any of my friends, it's over a burger and a beer, so I need to cut down a lot on that. I'm not a good cook, so whenever I go out for food, I know I'm getting something better than I would be at home. And now that I'm living by myself, I'm eating meals meant for than just one person, and that's not helping at all either. So now I've gotta stop eating everything I cook and throw some away or refrigerate it for the next day.
And once spring FINALLY comes around, I'll start running 5-10 miles a week again.