It's more work, but when you vote it would be nice if it popped up a short optional comments field. You can't force anybody to leave a comment (you can't force them to leave a legitimate answer, either). But it would be nice to see for each question/answer a list like this:
+1 worked for me
+1
+1
+1 concise
+1 new perspective, even if it may be not correct/useful/reliable
+1 insightful
-1
-1 wrong
-1
-1 i hate python
-1 confusing
-1 wrong
-1
-1 your an idiot
The more I use it, the more I think that Slashdot has the best discussion and moderation system out there. This is inspired by it, but in a Stack Overflowish way.