So there's this forum called Hackforums (hackforums.net). It's a pretty big forum, maybe a little bit bigger than Newschoolers. They have a rep system, think like our karma system but it's only based on what people give you, not your posts and threads.
Only upgraded members can give rep (it costs money to upgrade), and this rep ranges from -3 - +3. Now here's the key part, it's all PUBLIC. Everyone can view who gave rep and why they gave it. People need to include a reason.
So obviously reputation points and upvoting/downvoting are not completely the same, however I feel like that publicness could help make people think before downvoting. Wouldn't people be scared to downvote someone for no reason if they knew that their downvote would be public? Maybe don't include the requirement of a reason, as that could take too long for people, but I think if there was a button to view the downvotes, people wouldn't fraudulently downvote as much. Just an idea.
Maybe it wouldn't work or people would be against it, but that's why I want to see what people would think of it.