I've always found that slashdot's moderation system does a great job of handling that particular problem by allowing users to be modded "funny" in particular, m

I've always found that slashdot's moderation system does a great job of handling that particular problem by allowing users to be modded "funny" in particular, making it not count for anything, and allowing users to add a moderation modifier to "funny" moderations (so you can redefine a +1 Funny to be effectively -1 Funny, if you wish).