My OH has been going for six weeks on SW, he lost a stone, but last week although he did nothing different, he put on four pounds!! He merely eats fruit all day and has a fat free meal at night, usually out of the SW recipe books. Not sure it is working for him now, and all he lost at the outset was water.
As pasta freak says, I think it is better to stick to non processed foods to lose weight. A friend of mine has done it through a dietician and lost loads without cutting out her favourite foods, she just cooks everything fresh and nothing comes out of a tin, packet, or the freezer.