I've had my PB for more then a year and my palms haven't showed any signs of discoloration. I'm sure this isn't an issue with the MBP's. But, I think it was an issue for the iBooks, and probably is an issue for the MB's. Wash your hands more often, imo :-P
i was under the impression that the mbp are metal, and not painted?
if that was the case, they might show a smoothing effect, but loss of paint would be impossible? ill be looking at the pro's to replace a macbook. love the little guy so much, may go for another mb again though..