I only wear a watch (with a non-metal band) so denting it up isn't a problem, but the oils/sweat from my hands is when I've been typing for a few hours. It has now corroded one of the palm rests on my MacBook Pro. I've heard Apple will replace it under warranty, but that involves shipping it out, and blah blah blah too much to bother.
Said corrosion is small black dots near/right on where the metal palm rest meets the edge of the plastic lip, right above the CD drive.

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