I read Supertraining cover to cover (twice) for no reason other than to be able to look cool, and stand on even ground with some of the more pretentious folks at Perform Better.
A few gems, but largely impractical; I would have a hard to saying how my methods would have differed if I hadn’t read it, but probably not much.
I don’t think I’d call it a waste of time–BUT it hasn’t made me any more money, or gotten me any more laid, or really gotten my clients better results.