i was hypnotized once a long time ago, which was enough to convince me that it is real. I taught myself to do it, and I hypnotize someone else on a regular basis. Let's just say it makes for really, REALLY good sex. you say "come" and they say "how high?"
there are some who believe memories "recovered" during hypnotism therapy sessions can't be trusted, and I tend to agree. however, i think that hypnotism does have a place in psychotherapy, for the simple reason that it allows you to interact with a person's unconscious in a very hands-on way. i have had some amazing experiences talking to isolated segments of people's personalities (they give themselves names!) and reasoning with them to help change a person's overall behavior, as well as talking to recurring dream characters. there's no way to prove what was actually going on, but it was very interesting and sometimes productive. hypnotism is also great for pain control. there are some who prefer self-hypnotism to general anethesia, though i wouldn't be so brave.