I think Azarthoth is back too, and I think I know which account, but I don't get the impression that the mass upvote sockpuppets that were suspected to be helping his previous incarnations are active.

I think there should be simple ways to combat this sort of problem anyway, for a start people's accounts could list the percentage of upvotes you give in the same way it currently lists the percentage of upvotes you receive. Limits could be put on the amount of downvotes you can issue by saying that they cannot exceed your karma (or a multiple thereof).

This problem has been encountered before in places like reddit - how did they deal with it there?