Yes for the unibody Macbook, not so much with the White Macbook. No matter how much you try, the white plastic where your palms rest when typing discolor after several months of use, and can't be cleaned. It looks rather nasty.
Working in a huge IT department, which serves 20,000+ users, and has ~ 35% Mac users, all of the white Macbooks are discolored in the palm area. Some are downright gross looking, and I use a USB keyboard/mouse, so I don't have to touch them.
Have you tried a Mr Clean pad?