Imagine a system that works like this:

• upvotes - a simple click, as it is now
• downvotes - you click the downvote button, and then specify a reason from a list (disagreeable, unfunny, inaccurate, off-topic, rude, disingenuous, etc.)

So it's a bit like Slashdot, but only for negative reactions.

Each "reason" would be a dimension, as now you can measure content by funniness, accuracy, etc. And one of the effects of this system is that, if you are being downvoted, you'll have a better grasp on why. It's considerably more useful as feedback, for users in good faith.

(It has a few additional advantages too; for example custom sorting filters, and the very fact that a downvote takes a tiiiny bit more effort than an upvote should encourage positive feedback over negative one.)