When I was in college (bachelor's and master's in psychology) I took several "cognitive therapy" classes that included progressive relaxation and hypnosis. The "deep" hypnosis that involves suggestions regarding not remembering the content of the sessions, etc. are not really a part of "normal" hypnosis. One session hypnosis, is also pretty much useless.
Hypnosis, can be pretty effective if done regularly (which is why legitimate hypnotherapists will give you a tape, and/or want you to come back for future sessions). Self-hypnosis is easy to learn, and can also be effective, but since hypnosis is a "mental exercise," it's very much like physical exercise, "finding the time," and "getting into the habit", are the hardest part.
Also, effects are generally going to be mild, not dramatic, especially at first, and you can definitely "outwit," the hypnosis without much effort, so it's definitely a tool, not a cure.