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You could also have a probation period for new users. Say for example no posting new links until some minimal number of 1 point or higher comments (1 is probably enough at current activity levels). Eventually spammers will game this system so then you up the requirements to 1 point from a user w 3 or more points. 2 points from different users. There is obviously a point where it's too invasive so you have to balance it out based on how motivated the spammers are. At the current volume you could probably manually promote threads to the front page. At 5-10x the users that's not viable but that gives you some time to fine tune a better algorithm