I have no personal experiance with them, but I've never heard anything good about them, either (posts in this thread aside). I lost 30 pounds with Weight Watchers and have kept most of it off for about 18 months (gained back 5 pounds). I like WW because it teaches you how to eat for the rest of your life, both by portion control and by making healthier choices. It makes you read lables and makes you use portion control, but at the same time you can eat ANYTHING you want. It's a point system, you get so many points a day, and differant foods are worth differant points. You can eat any combo of foods that equals your points for the day, and you can save un-used points for a treat later in the week. You can do this program online only (that's how I did it) or you can do it by going to a meeting once a week. Over all, online is cheaper but many people like or need the accountability of the group meetings once a week. Either way, it's cheaper than just about any other diet program like LA Weight Loss or Jenny Craig.
If you want more info, feel free to PM me!