Perhaps karma should be subject to gravity. Login is required to view HN. Submitting comments and links is expensive while lurking is cheap. Perhaps 5 karma points buys you a comment or submission; 1 karma/min to lurk.
Just as we [ought to] only make things customers would pay for, we should only submit things users would pay to read. While Hacker Monthly does do this in some fashion, I don't think we should have to pay with monetary currency--but in cpu time.