The app is at: http://www.myfitnesspal.com/
I'm not good with the entire idea of dieting. I'm not going to stop eating chocolate, bread, or pasta. Low carb? Nope. And I love beef, chicken, and fish. Since I'm not going to change the "what" of my diet, I might as well monitor the "how much" to see how far over my ideal caloric intake I might be.
The iPhone makes keeping the diary of our meals easy. If this helps me lose five to ten pounds, I'll be sure to let people know.