Thierry's last post raises the interesting possibility that consciousness is some sort of highly developed epiphenomenon of the physical brain which reaches such critical mass as to exist on its own. I think this would also imply the interesting consequence that all life forms, from a virus upwards, and perhaps all matter, potentially possess consciousness and free will. I think, in fact, John Conway has proposed some such conjecture recently, though I have not read any details. This would be rather nice, as it would mean that the universe would be somehow "alive" in a sense we hadn't realised.
Marvin Minsky, I believe, at one stage asserted that computers would one day attain this critical mass and become conscious. I don't know about you people, but I have difficulty imagining this myself.