Or limit the number of votes one person can give to another within a time period. I think most vendetta voting happens in the heat of the moment. I don't like not being able to vote old comments, or skewing the voting on either side.
I like this fix. If the mass voters tend to have low karma, you could also make this a fix that only applies to people below some karma threshold.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.