We have a few threads about Slim Fast in our General Diet Plans forum that might be helpful. We've heard mixed reactions. Some people may lose a few pounds, but I think most people give up on it quickly because they are hungry and bored with it. There isn't really anything special about Slim Fast to make you lose weight, it's just a controlled amount of calories for your meal. You can accomplish the same thing by eating a frozen diet dinner, yet it will be more satisfying. Slim Fast has a very high failure rate for this reason.
If you decide to try it and want to find more people that use it, you might post in our General Diet Plans forum for support from other SlimFasters. In the meantime, check these threads for input from other dieters:
success with slim fast?
Slim Fast Anyone?
Is Anyone Doing Slim Fast?