There are issues with both sides of the down button debate, but I'm more for it than against.

For a different take on the downvote button, yesterday I put a post up on a technical thread. I hadn't really read properly what the discussion was about, so my post wasn't really helpful even if well intentioned. I only noticed when I got a couple of downvotes. I looked again at my post, then at the OP, then realised my error. Eventually I deleted my post. So, in that instance, I found the downvote helpful to myself as well as for the rest of the thread: make sure I read the OP carefully. ;-)