Just to counter to the SuperSize Me results. There was an Iowa Teacher who conducted his own experiment with McDonald's. He had different rules, since he limited his daily caloric intake and started exercising, but the results are very interesting.
http://youtu.be/wST4NxoiDcc
Keeping it simple may be the best approach at first: calories in/calories out. You burn more than you take in, you're definitely going to lose weight. Of course, exercising will also help with the weight loss, but there are many other benefits to exercise as well. I also believe that the emphasis on low carb, high fat or protein isn't necessary, but does help people limit their caloric intake. I've heard people around me swear off sugar because the paleo diet worked so well for them. I think that's good for them, but you do not have to follow that type of diet to succeed in losing weight and maintaining your health.
I think that the different opinions in this thread can all be correct, because there are many successful ways to tackle this challenge.
I exercise a lot. I've been doing bodyweight exercise, running, heavy bag work, and swimming. Currently training for a half-marathon and I also cross-train. So I'm exercising 6 days a week. I try to eat good natural food, lots of veggies and fruit. However, I also throw in some sweets, a lot of carbs (love rice and bread) for an energy boost the night before a run. On my rest day I am mindful of not overeating because I don't want my next workout to be very difficult. My thoughts: screw motivation, routine creates habit and this all requires discipline. So, I think discipline is the most important thing. I feel much stronger now, nearing 40, than I did when I was 20. My main concern now is to avoid injury by not overdoing my training!
I rarely post here because I've been spending a lot of time lurking reddit fitness, running, and swimming. Check it out if you're interested. Lot's of interesting stuff to read.