Do social sites with karma need a decay function?
walterk: I would just hide (not remove) karma entirely.  Submissions, comments, and users.  That removes the incentive to game for karma and mitigates against the bandwagon effect, while the karma system still determines placement of submissions and comments within their respective threads.  And I'd argue that high placement is reward enough in itself to promote meaningful contributions.  Obviously, people can still try to game for placement, but it's less interesting when it doesn't contribute to an overall user score.Anything having to do with a leader board, in contrast, simply encourages people to game for karma.