Camera Labs has posted a comprehensive review of the new Canon S100 and it's looking good.
Truly, Canon has done very little to beef up the actual camera. They have expanded the zoom range of the camera slightly, from 28-105eq/mm to 24-120eq/mm, but that has come at the expense of quality. DPReview's camera comparison shows that the new lens is much softer than the old one, which wasn't exactly tack-sharp to begin with. This of course means that the extra two megapixels in the S100 provide nothing except for larger file sizes.
I wish that Canon had gone the route of Olympus and attached some better glass. The Olympus lens is so good that it outweighs a sensor that is a step behind almost every other sensor in the high-end compact market. Granted, the XZ-1 is a bit larger than the Canon, but they should have, at the very least, kept the lens as good as the previous-gen S95. Canon's JPEG processing remains good, so if you are in the market for a super-compact camera, this should certainly be on your short list. I would still take the Olympus XZ-1, though.