There's been some discussion of it over in ideas for Snapzu and elsewhere. There are some really good points as to why identifying where a down vote came from would be a bad reason as it opens the door for abusive of harassing PMs and the like and the down vote does have a legitimate function so it would be poor form to make people "afraid" of down voting something even if it's for a good reason.

I'm still torn on the issue, but at the very least make it mandatory to specify a reason for the down vote. If there are a couple that indicate it's in the wrong tribe, then the poster knows how to fix it.