Hi! I do use slimfast, mainly for breakfast and occasionally for lunch or dinner (if I'm on the go and don't feel like making dinner or am not as hungry). I do like that slimfast has lots of the nutrients I need- it seems like a lot of the time, if I don't do that or take a vitamin, I'd be missing out on a lot of that.
The optima shakes are great at keeping me from getting hungry, but I wouldn't use them as my sole source of food! One shake a day, some days maybe two shakes- but be sure to get at least one real meal in there a day. Just doing slimfast won't teach you to eat right! It just teaches you to drink from a can!
So far, I've lost 30 pounds- so I'm doing something right! But I get exercise in there too, am not relying on just my diet (mainly because I love a nice dinner- and even though I eat much less than I used to, I suspect I probly get a few more calories in on the weekends than I want to admit, and I gotta burn 'em off somehow!)
Good luck!