Bryan links to this also, but I want to make sure you don't miss it: Angels and Quanta.
Classical physics describes a universe which is predetermined by its initial conditions. If every event is absolutely determined by its preceding causes then everything that happens – including me writing this and you reading it – is inevitable and our free will is no more than a useful illusion. The future has already happened.
In other words, if there is only cause, there is no motivation. In practice, no one believes that, including those who preach determinism
I think it is important to remind everyone, as was pointed on what this post linked to, that "Libet himself was not a materialist at all. Apparently, he thought consciousness was not an epiphenomenon and might even survive brain death."