3. Norms and practices. Bloggers have undermined the blogosphere. Bloggers do not link to each other as much as they used to. It's a lot of work to look for good posts elsewhere and most bloggers became burnt out. Drezner and Farrell had a theory that even small potato bloggers would have their day in the sun, if they wrote something so great that it garnered the attention of the big guys. But the big guys are too burnt out to find the hidden gems. So, good stuff is being written all the time, and it isn't bubbling to the top.
I write as much as I ever have, but in my posts I link more to news sources and less to other bloggers than I used to. I'm not sure why. Part of it might be related to another evolution I've noticed: the political blogosphere increasingly seems to latch on to four or five outrages of the day that suck up most of its attention. It seems like every blog I read posts about the same few political nano-scandals every day, and since I mostly find this stuff kind of boring I don't link to it very much.
I don't know for sure if that's a real trend or not. My memory is famously fuzzy and I have a hard time really remembering what things were like four years ago compared to today. But whatever the case, the end result is less engagement with other bloggers and less conversational tone to the blogosphere. That may or may not be entirely a bad thing, but I kind of miss it.