I've learned a lot about "diets" over the past few years. Basically, if you follow almost any of the brand-name diets you will lose weight. The problem is that eventually, you will want or need to go back to eating in the real world and the weight will come right back. I tried Slim Fast and lost some weight, but when I started eating normal food again it all came back (and then some).
Ther real key is eating fewer calories than you burn. It sounds very simple but many of us still struggle with mastering the concept! My goal is to stop trying "diets" and try to learn to eat normally and exercise more. That said, I have been drinking Slim Fast on the way to work some mornings. It's easy to grab and keeps me full until snack time. I think the shakes and bars can be useful if you need something quick, but I know I can't stick to the diet and keep off what I lose!