I've used some of the files from warpmymind.com, and found that, with a bit of practice, they work moderately well. Admittedly, I haven't done any of the more extreme ones, just basic inductions, and one that's supposed to make you horny, but I've had a good amount of success. The tricky thing with hypnosis is that, in order for it to work, you have to both want it to, and believe that it will. If you go into it skeptical, you won't get very good results - or so I've found. It took me a while to get used to the frame of mind, and I'm still not very good at it.