Well, on-line support seems to help big time. In 1991 a Brown University study found that people who used the Internet for support around weight loss actually lost 3x as much weight as those people who used the net for information only.

It was a low-fat diet they studied and folks lost an average of 9 pounds if they used the Internet web site the study set up for support and 3 pounds if they did not. The more frequent the participation, the better the weight loss. The support was from professionals, not peer support like here, but I am betting there is some generalizeability.

Has anyone ever looked to see how many people who joined the forums on the same day they did have disappeared? Some (in fact a lot) signed up and never came back even once.

See the study