One way could be to reward "early promoters", eg. give karma to the first users that up-vote a story, which later makes it to the front page or reaches a certain number of votes.
( http://en.wikipedia.org/wiki/Keynesian_beauty_contest )
One way could be to reward "early promoters", eg. give karma to the first users that up-vote a story, which later makes it to the front page or reaches a certain number of votes.