A number of users have observed that when people down-vote questions or answers most of the time they do not leave any comments. This is a problem because this does not give the user or who asked the question or gave the answer to fix the problem if there is one. So what I thought about is a feature that will activate when someone down-votes a post, when someone downvotes the comment feature automatically opens and says "Please explain why you down-voted". I found this in an answer on the OSQA meta site, I am not quite sure how it can work here, but perhaps it can be used:
I do not mean to make it mandatory for a user to give a comment, no rather just give the option and the reminder.