I'll add my anecdotal experience to this too. I had to have the whole keyboard replace on mine last week because of a stuck b-key. Fortunately it was still under warranty through work. As of last night some miniscule crumb has got behind the up-arrow key and I have the same problem again.
Yeah.. try cleaning it with a finger nail or piece of sturdy paper. Even though it looks like not doing much, this regularly fixes my problems. Perhaps the crumbs are just pushed inward.
