Ask HN: good examples of discussion voting systems?

The recent post and HN comments about social knitting network Ravelry got me interested to understand better what dimensions and approaches there are in discussion voting systems. I'd be interested in any kind of examples and analysis of successful discussion forums with different voting systems. As we all know, Hacker News has upvotes and flag for posts. For comments there is up and downvotes . If I recall correctly, downvotes and flagging are disabled until you have enough karma. The etiquette is to use downvote for posts that do not improve the conversation or are incorrect, but not for the disagreement. Ravelry has Agree/Disagree, Educational/Interesting/Funny and Love. It's interesting that the only negative one is Disagree, which is quite polite, but still causing occasional heat on Ravelry forums. I don't know if long-time Ravelry users have some flagging capabilities. What else is out there? TED has Like and Flag for comments, more rich system for videos. I don't remember all the details of Slashdot's moderation system, but there was labels like Informative, Funny and scores, but ability to give score was somehow based on how much score you had got.