I guess that might be going a bit overboard. But it's not completely unprecedented.

Slashdot, for instance, has a restricted tagging system for their comments. Comments can be tagged as "Interesting", "Insightful", or "Funny".

I've heard some people on Slashdot complain about the "Funny" comments, but it's quite easy to filter those out via Slashdot's interface. I'd say that was pretty useful.