This is one of my only complaints about the mm Besides that I think its a very nice piece of hardware.
I guess I tend to be a bit lazy (and the nearest Apple Store is in Indianapolis, which is like an hour and a half away) and I've just gotten used to cleaning it.
When it sticks just flip it over in your hand and scroll quickly and forcefully. I do that for a few seconds maybe once a week or two and mine works fine.