I've never really 'got' free will - why it is so mystical and important and controversial. Maybe it is just that I don't see what the problems with determinism are supposed to be. As far as I can fathom free will is supposed to be the sense that we make our own decisions free of external causes, that we are the agents of our own actions. Sounds fair enough - but the problem is supposed to come when you add in determinism - apparently our thoughts and actions being causally determined by, e.g., our brains, is incompatible with our free will, with us being these free agents.
This leads some people to reject determinism in the favour of absolute randomness (something that is patently absurd), or statistical probability (e.g. quantum mechanics). Dan Dennett devotes a whole book (Freedom Evolves) to this question, I've only made it halfway through (busy man me), but I've heard him talk on the topic before. Dennett argues that in the random probability model the undetermined bits are precisely the types of freedom that are not worth having (Descartes has a similar point about the poverty of real freedom in choices made in the abscence of evidence or impulsion to one side or the other).
I have to agree - but I think that the impulse to embrace randomness to salvage free will from determinism highlights the fundamental misunderstanding that lies at the heart of the free will problem. Many of those that reject physical determinism - the idea that the brain gives rise to the mind - accept non-physicalism instead, they believe that the mind being something other than physical somehow frees them from the problem of determinism. But it is far from apparent that it does any such thing if there are causal factors operating in this mental world (and we have every reason to think that there are - from the physical input via the senses to the interaction of mental properties). It is hard to see how, if the mind is made of causal 'stuff' at all, how it can escape from determinism.
It reminds me of Nagel's famous question, "What is it like to be a bat?" - which assumes, for an answer, that it is even meaningful to ask how one mind-thing might gain access to being another, different mind-thing - the underlying assumption that you could somehow constitutively 'be' another thing, whilst retaining something of what you were before - the assumption, in other words, of a animating spirit or homunculus piloting the show (Nagel is actually using the argument to try and show that subjective experience cannot be reduced to a functionalist explanation).
At some point, one would think, there can be no more little men behind the scenes pulling the levers - something must be animating him - at some point the causal explanations must be grounded. Rejection of determinism just seems to be a refusal to begin this endeavour, a belief that if anything causal underlies the actions of a mind they somehow become unfree, because they are caused by something other than that mind. But, of course, they are not determined by something 'other' in a meaningful sense - the mistake is to confuse layers of explanation - when my arm lifts a glass - that the action is caused by the contraction of muscles, or, deeper still, by myosin sliding over actin, does not make it any less my arm that is doing the lifting.