I remember that many Witnesses did not approve of Anthony Robbins because of his practice of walking on hot coals. Many were convinced that he was "demonized" because of this. The interesting thing about firewalking is that even though it has been practiced by tribal religions for ages, there is really nothing supernatural about it. Michael Shermer, who writes a monthly column in Scientific American magazine wrote an entire article on the subject. He also wrote about it in his book: Why People Believe Weird Things. He wrote about the physics of hot coals and how people do it without getting burned. Shermer who is a self-proclaimed skeptic even did it himself without getting burned.
Another interesting side note about Robbins. In his book Unlimited Power, he quotes from the December 22, 1982 Awake magazine. His reference from the Awake had to do with diet and health. Interestingly, Anthony Robbins has recently published updated information and given lectures where he has recanted much of what he used to teach; admitting that much of it was incorrect.
I didn't find his books very useful or practical, but in my opinion his audio program: Lessons In Mastery is an excellent program that I think would benefit anybody.