A really interesting idea, perhaps the easiest way to do it would be to order the nodes by some kind of decayed reputation, for example:

    $decay_rate = 30;
    $score_for_order = $reputation / (2 ** ($days_old / $decay_rate));
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This would make a reputation point from 30 days ago worth half what one from yesterday was. I would think it should be a simple matter to add this option