I recently have come across a superb documentary on Google Video (really the only thing I use that somewhat drab service for) discussing the potential of artificial intelligence, both in enhancing humans, and in replacing them (see it embedded below).
This documentary, entitled "Horizon - Human Version 2.0" by BBC discusses the eventual "singularity", or point at which our understanding of the human brain and capabilities of computer processing power will converge to allow us to "download" ourselves, that is, our brains, into computers. It is a truly fascinating documentary and I highly recommend watching it.