Join Date:Joined: Mar 2011
The grey one S is using anodized aluminium and has no chipping issues.
The black one S has a MAO layer, which has chipping issues, however, HTC quickly fixed it with newer models that had smoother/rounder edges and a bevelled USB port so the chipping didn't happen by itself. Saying that, I have had my one S since April (the first version) and it is still in perfect condition except the edges of the USB port.
AFAIK, the black "one" does not have a MAO finish.