The recent implementation of a -5 karma penalty for replying to comments that are at -3 or below has clearly met with some disagreement and controversy. See http://lesswrong.com/r/discussion/lw/eb9/meta_karma_for_last_30_days/7aon . However, at the same time, it seems that Eliezer's observation that trolling and related problems have over time gotten worse here may be correct. It may be that this an inevitable consequence of growth, but it may be that it can be handled or reduced with some solution or set of solutions. I'm starting this discussion thread for people to propose possible solutions. To minimize anchoring bias and related problems, I'm not going to include my ideas in this header but in a comment below. People should think about the problem before reading proposed solutions (again to minimize anchoring issues).
Solution: Ban their IP addresses. This actually works, I'll tell you why. Not because they can't get new ones, but because they can't infinitely get new ones. If you've ever sought an unsecured proxy (a key way of obscuring your IP address) you'll know that it's tough to find a good proxy, they're slow, and they frequently leak your IP address regardless. Even programs like Tor only have so many IP addresses. To make it worse, (for them) it's no fun to use proxies that are far away - they're slow as all get out. This technique worked on spammers on a forum that was growing fast. It took a while to collect all the IP addresses they were using, but it was an extremely effective method of stopping spam. Banning the account will make this more effective. Doing both will make it a real hassle for them to post, and after a while, it will be hard to find good proxies.
A solution also requires that volunteers from the forum / moderators can ban the trolls.