Karma and all sorts of voting in general have a flaw: they reflect Average Joe's opinion unless, of course, you have a narrow social/professional group as your user base. The broader your group the lesser are standards of your social website unfortunately. Wasn't it one of Reddit's lessons?

That's why I think there are two types of winners in this game: those with good implicit ranking mechanisms (Google, Flickr) and those with good human moderation (Slashdot). Those based on explicit voting are taking the risk of being taken down by broad and unfocused masses.

Well there are a couple solutions. One, you could tabulate votes based on the karma of the users. So someone with higher Karma gets bigger weight. That will probably focus the discussionsa and submissions a lot.

Two, you could have interesting comments, based on people voting them up or down, and their replies.

Also you could do some kind of geomtric progression instead of linear, or combine that with the voter's own karma.