This one's been bugging me for a while.
Many times, people will vote on my answers, and then I'll edit it afterwards.
They should be notified when I edit it, so that they can choose to see if they still agree with their vote, in light of the changes made to the answer (or question).
Unless I'm missing something, at the moment the only way to tell if the answer was changed is to go to the page and see if it's been edited since you voted on it.