zlacker

Find some way of qualifying upvotes by who made them, at what point in the lifetime of a comment and each upvoters upvoting frequency. Use these factors to adjust the score, rather than just a score+=1.

A user who upvotes ten comments a day should have far less impact per upvote than one with very high karma and a high average score who only upvotes infrequently (and is not involved in the thread).

I realise that you're asking about comments; I think that this applies equally to story submissions.