I read an article a while back saying that hypnotism works great with most issues as long as the client wants help and is willing to accept the change. If you fight it or don't really want the help it may be a waste.
Jocab is right on the mark: hypnotism is great but it may not be enough in itself. A friend of mine had several sessions of hypnotherapy for smoking and alcohol addiction and was unsuccessful. The problem was that it was his wife who wanted him to stop; he wanted to party. So, after a few weeks, he was back to his old addictions and blamed the hypnotist for his failure.
If you really want to quit you'll find hypnosis is like a magic carpet to take you where you want to go.
You probably need to know that hypnotism has evolved over the years. If you've got a mental picture of some guy with staring eyes dangling his pocket watch on a chain, you're thinking of the system developed by Dr James Braid, a Scottish physician, back in the 19th century. The same method is used with just voice and you'll have seen that on the movies or TV.
Something you need to remember is that it won't be done in one session -- if that habit-pattern you're trying to lose is very deep-seated it's going to take a while -- so you need to check the probable cost of a course of treatments with the therapist.
Yes it definitely does! It depends what you are dealing with but hypnosis is very helpful in almost all cases. Try listening to a hypnosis MP3 download first and see how you respond. There are a lot of them out there for all kinds of problems.