Anyway, when I'm using a wristwatch I don't have a problem with the case, but the strap is often itchy (not to the point of irritating the skin, though)
It's possible. You can nickel treat alu to give it a consistent durable finish as alu oxide is quite easy to dent and this deposits some on the surface.
Another thing I've seen is that a friend of mine's MBP has started to dissolve. It is pitted and looks burned. Turns out some people's sweat eats them as well.
