Just wanted to mark down my thorough delight with the down voting caveat encouraging the voter to leave a comment. I wish that more sites would employ this. From what I recall it entreated me to add some constructive criticism in a comment.
I know this is a long shot, but I wouldn't mind having this coded to a preference which defaulted to that popup needing closed. My thinking there is that new users may be helped in curbing their down voting tendencies by having a dialogue that must be closed.
Seasoned users, of course, should feel free to forgo the advice since their level of contribution is indeed less questionable.
It's great and I give it many +1. Kudos!