The Magic Erasers work wonders, I use them on my MacBook every month or so, and they make it look brand new. Since I replaced my stained palmrest, I have had no problems with staining, though I do now have a huge smear of adhesive from where I removed a palm rest cover (it was getting stained).
As far as the keys go... they get no dirtier than any other laptops that I have seen, and the trackpad develops that worn down shiny look to it after a few months, but that is because you are using it.