I've noticed it as well. I'm not sure if this is due to an increased amount of criticism or if the quality of the articles posted has gone down, warranting more criticism.
The more blog drama (AA killed my dog!) which gets through, the more people who like blog drama are drawn to the site and up-vote it.
If I were PG, I would look at the data and try to categorize the type of submissions which draw the most negative comments (and I think we still do a good job of -4'ing useless comments) and set a high threshold for a story of that type to get through to the front page.
As another example, if submissions about 37s tend to be really vitriolic, make it harder for those submissions to get through and make it harder for people with a history of incendiary -4 comments to post in them.
The bottom line is that there is a lot of data collected here which can be used to optimize the content towards quality, since we all seem to be talking about the same thing when we talk about quality.
I've noticed it also. When I first joined people really took care that their comments were thoughtful and respectful, even if they were disagreeing. Is there anything to do other than to personally try harder to be thoughtful contributors?
Those comments are still there, just a bit less obvious.
I figure it is because the "original" members were of a certain level of contributor. "hand picked" in a sense (classic early adopters). A these move on to pastures new and a large numbers of new people come in you start to get a range of commentary style rather than just top class stuff.
(not that all newcomers are bad - or indeed not that many of us are - just that you get a range of attitude).
And of course almost outright trolling is less obvious once the general range of commentary style is expanded; so it passes off as serious discussion.
