For the most part I think that hypnosis works to a certain extent. When we think about hypnotism in mainstream media / popular culture etc, we tend to think about people being entranced and doing things against their will. This really is not the case.
Hypnosis does put you in a trance like state but it can't make you do anything that you don't want to do. Hypnosis works on the power of suggestion, and draws its power on your willingness to want change; Hypnosis will suggest to you courses of action but in the end you make the decision as whether or not you want to change for the better.
From what I hear, hypnosis does not work for all people. I think that it may work partially from placebo effect. One time, in school, a hypnotist came as an entertainer for a school function. Of the 15 the students who volunteered to be hypnotized, all but 2 gave positive testimonials about it later, saying they felt they were more relaxed.
So, I think there is no harm in giving it a shot... From what I see it can do genuine good. You never know, it may help you for a turn for the better.