Did you spill Fanta on the keyboard?? seems to be a popular right now.
Anyway, I'm not sure about the macbook (mine is in delivery limbo ATM... boo!), but on my other laptop I use the Lysol kitchen/bathroom wipes and have had pretty good results.
OR... if this is a new macbook, I've read a few threads on people getting new ones with 'crooked' keys. Might want to take it back to apple for fixing...
--rob