Hypnosis itself is neither dangerous nor safe. It's based very heavily on the belief of the subject (the person you're hypnotising); you'll find that in general, a skeptical subject will be harder to hypnotise than an open minded and willing participant. Because of this, if the subject believes that something could go wrong, there is a chance that it could (or the subject just won't allow themselves to be hypnotised at all). Hypnotists usually give what is known as a pre-talk to dispel any fears and misconceptions that the participant may have about hypnosis. If done properly, this should be enough. With the exception of that, the only real dangers will occur by poor communication on the part of the hypnotist, and are not because of hypnosis itself.
One other thing it's worth being aware of is a phenomenon called 'abreactions'. From what I understand, these are very rare, and are caused by a subject having some bad memory or experience triggered whilst in hypnosis. They involve subjects becoming incredibly emotional. There are ways of dealing with abreactions, on the off chance that one will occur (as I said, it's rare) but you should know what to do just to be safe.
I don't own the Manchurian Approach, but have heard very good things about it. As a dvd about hypnosis, it will probably cover any worries you may have about safety and whathaveyou, but if not, more information is available from a quick google search. Really though, hypnosis is not dangerous, assuming the hypnotist is competent and can communicate well with his/her subjects.