I have talked to people who had success using hypnotherapy to quit smoking or for other health related issues such as chronic pain, but I haven't met anyone who used it to lose weight. I know that many top atheletes on the professional sports team undergo hypnotherapy as well as top CEO's and such. While I definately do believe this a part of holistic medicine, I don't think it is has any similiarity to quacky diet pills. I just looked it up on wiki:
http://en.wikipedia.org/wiki/Hypnotherapy