Some of you may have heard of this problem with aluminum PowerBooks -- corrosion or "pitting" of the aluminum surface to the left and right of the trackpad area. But you've never seen a worse case than my poor little 12" PowerBook. I bought the machine in October 2003. Within 6 months the spots had emerged; as I approached the end of my 1-year warranty period (no Applecare) they had progressed to the advanced stage shown in the photos below. Apple Computer kindly repaired my problem under warranty. My palmrests became sleek again and the corroded part was sent back to Apple for "analysis" or something.
A year after the repair (October 2005), significant pitting was visible again. Updated photos to come. It's no longer my primary machine, having been replaced by a 15" model (with Applecare!) which I am striving to protect from a similar fate.
The epicenters of the two problem areas map to the bases of my palms at rest. Apparently my body chemistry is on the caustic side -- must be all those Sour Patch Kids.
And I haven't given up on that idea of a sideline business that makes replacement palmrests from birch veneer.