Sometimes Q/A gets some downvotes and some users will complain about the down-voters "not having guts to say why". We all have seen that.
Now, for example, I believe that there are often good reasons to downvote, but also good reasons not to spam comment field with things that are either obvious or already stated in another comment or in policy or FAQ. But I agree that it can be frustrating.
But this suggestion is not about solving this issue.
It would be nice if users were given option to Tweet/Facebook/whatever about votes, exactly as about questions.
This way, when I downvote, I could tweet why, when I upvote, I could tweet why, but not because I'm trying to help the conversation (in which case I'd definitely need to post actual comment), but just because I feel like that. And most of all, I could do that in consistent way (just think about it like committing).
And finally (I'm no PR expert, but) it couldn't do harm to SOFU outside it.
Edit: Apparently (again) I did not make myself clear. The suggestion was not meant as aimed specifically at downvoting, but at voting in general. It wasn't meant to encourage any kind of "LOL, look at this n00b" behavior which we all are happy we don't see (or at least manage to effectively sweep off) here on SO.