I've had several unexplained jumps in karma over the last few days, amounting to around 80-100 points. Someone else mentioned the same, and I believe it's happened to quite a few people. If that's a side effect of reverting the votes of systematic downvoters, fine, but if we now have a systematic upvoter, I really don't want to see this. It doesn't have the same emotional overtones as downvotes, but it obscures the signal in the same way.