What do you think about http://arxiv.org/abs/quant-ph/0604079 ? Let me explain how I understood it, but it is possible that I misunderstood something. In simple terms, the theorem says the following: If humans have free will, then the rest of nature is not deterministic. But if you treat humans on an equal footing with the rest of nature, then this theorem can be further simplified as: If there is free will, then something is not deterministic. Sounds almost like a tautology, doesn't it? But of course, every theorem can be viewed as a tautology by those who understand it very well.