When Jesse gave me his Macbook it was partially for work and partially so he could get a Macbook Pro to help his RSI. You see, the Macbook is just the right size so that a lazy typist will lean their wrists right on the edge of the machine. This wouldn't be so bad except that unlike every other thing produced by Apple they decided to give the Macbook a sharp edge. Not just any edge, but one that's rough and serated for maximum wounding. My right hand started to hurt after a couple weeks of this.
Fortunately after a simultaneous failure of the DVD-R drive and the hard drive (and the upper case is being replaced because of yellowing and the lower case was damaged by the last DVD-R drive replacement) I'm back to my iBook. For about a week the screen seemed big and goofy and everything was sloooow but I'm reaclimating. But my wrists love me for it.
EDIT: They replaced the whole thing, saying that its too new to have had so many failures and they didn't want to leave me with a lemon. Say what you will able Apple's hardware, but their service is pretty damned good.
Once I get it back, I dunno... sandpaper? The machine doesn't close too tightly so I could glue a thin wrist rest over it?
EDIT: I'm glad to report that a simple layer of medical tape does wonders.
You'd think this would be something they'd catch almost immediately in user testing. Maybe all their testers have perfect typing posture. Maybe someone has to take Steve Jobs around town and remind him that round rects are everywhere!