How about something like Slashdot, where you can say why you are downvoting. +/-1 agree/disagree +/-1 thoughtful/usless "Thank you for your thoughtful comment

How about something like Slashdot, where you can say why you are downvoting. +/-1 agree/disagree +/-1 thoughtful/usless "Thank you for your thoughtful comment, but I disagree with your conclusion." "I agree that 'Palin Rocks' but your comment adds nothing of interest to this discussion."