If you've ever seen a used white MacBook, you know how grimy the wrist rest gets. Just gross. Whatever spongy rubber they use on the white ones wears down, gets sweat and goo caught in it, and no amount of Windex can bring it back to life. My girlfriend has one, and it was yucky looking.
So instead, I replaced it with the wrist rest/keyboard assembly from a black MacBook. She ordered it from this place. It was as advertised, seems to be the real OEM part. Took a handful of small screwdrivers and some patience to install. Now it's working great, and her computer now has a unique look.