This is a tough issue because the last thing I want is a notification when someone fixed a typo in their question.
Generally most of the edits I see to questions were either minor typo corrections or were brought on by a series of comments that occurred before any answer was written. In cases that someone did answer, it usually seems pretty clear to me that they shouldn't have answered until there was more clarification.
Now, there are cases that I have seen an edit to a question that does not fall into the circumstances I mentioned before and it would be very nice if there was an alert of the change. I also think these changes are the ones that are worthy of being bumped to the top of the front page. People before have recommended having some option to select if the edit is minor or major. If it is ever determined to have something like this added then I would be in full support of alerts when a major edit is made. But until then I think there would be too many annoying alerts for minor edits that it just isn't worth the feature.