amigabill is right on target here. Diamonds can be used as semi-conductors, with a little doping. They also have the best heat conduction property of any material known to man, so heat would be able to be sucked out of the cpu a lot quicker. And DeBeers is still holding the diamond industry by the throat, being a rich and very powerful company with many connections.
But creating diamonds still takes a lot of resources and energy. Creating silicon wafers is amazingly heavy on the environment, and diamonds would be even heavier still. It might be the electronics technology of the next fifty years though, keep a look out.
