I guess that I agree with Eliezer that the signal to noise ratio is not as good as it used to be, at least not as good as when I first joined here. But I'm not that highly active a user, and my karma is only around 9000, so my impression may not be that important in this context.
9000 is more karma than I have... and I've been here since the beginning! (I mostly write comments rather than posts, though, and you get more karma from posts, especially posts to Main.)
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).