It may not be worth the effort, but it would be interesting if one were blocked from posting as long as one's karma earned in past 30 days was < -30 or so. Might make it easier to ignore trolls.

I've been thinking something along those lines myself. Although it would be kind of awkward if one of us made a single main page post that people didn't find interesting and was downvoted just to -4. I think Eliezer and Luke may even have done that at least once out of all their respective posts. It just takes doing that once in a month that they haven't contributed much and bam, no more commenting for those top contributors for a month!

A solution that might work is having comments by < -10 total karma users greyed out or otherwise made less visible. Just any sort of automated troll warning system at all would be great!