Public user karma graphs for users as well as posts seem an interesting if slightly cluttering user interface addition [a neat little graph icon next to the quote bubbles and the chain link], that might help combat this while having the neat benefit of making it easier to infer all sorts of things.
I see my karma go up without anything on my first page of comments changing all the time; it makes me wish I could see all recent changes to my karma so I could go back and participate in any older discussions that might be re-opening.
People who go back and downvote every post or comment a Less Wrong user has ever made, please, stop doing that. It's a clever way to pull information cascades in your direction but it is clearly an abuse of the content filtering system. It's also highly dishonorable. If you truly must use such tactics then downvoting a few of your enemy's top level posts is much less evil; your enemy loses the karma and takes the hint without your severely biasing the public perception of Less Wrong's discourse.
(I just lost over 200 karma in a few minutes and that'll probably continue for awhile. This happens to me every few weeks. Edit: I mean it's been happening every few weeks for a few months for a total of only three or four. Between 400 and 700 karma lost total I think? I don't mean to overstate the problem.)