Ms. Hargittai has some very solid research here, and it certainly seems to be a good start on refuting Sunstein's theory. I think she's missing a larger and more valid response to Sunstein, though. One of the reasons a lot of conservative bloggers do what they do is that they no longer trust the MSM to give us accurate, unbiased information on either domestic or foreign affairs. Nor do they trust the "conventional wisdom" of the pundits who appear in the New York Times, Washington Post, or the talking heads that appear on the network talk shows. This distrust manifests itself in fact-checking their asses (as seen in Powerline's role in Rathergate) and by providing alternate channels of news dissemination, as with Arthur Chrenkoff's continuing "Good News From Iraq" linkagery and the similar, ongoing reports from milbloggers that report the full story from the front lines.
The question of whether rightist blogs are engaging leftist blogs (and vice versa) in a substantive matter is an important one, but I'd say it's only part of the big picture. Many rightist and libertarian blogs came about through disgust with how the news was being reported by ABCBSNBCPBS and the major metropolitan newspapers in New York, LA, and Washington; confronting, fact-checking and mocking the MSM was and is the main point of their existence. Dealing with Soros-funded blogs like Daily Kos and Oliver Willis (or their local freelance allies) was a secondary mission for many bloggers, though they could usually be relied on to take shots as opportunities presented themselves.
My experience in reading the various local blogs, as well as nationally noted blogs leads me to believe that the conversations and cross-referencing Hargittai is seeing are more the norm than the exception. Sure, there are blogs that don't do this - if this LJ ever transitions to a regular blog, I doubt I'd link much to los Rojos, since I find the MSM sufficiently irritating and I have enough friends & acquaintances on the Left to begin with that I don't feel the need to subject myself to Andrew Sullivan, Kos, Josh Marshall and their ilk. On the other hand, I don't think black conservatives like Cobb and Avery Tooley get half the attention they deserve, even from their fellow pachyderms, so I'm going to link to them whenever I see them throw up something I think other folks need to take a look at. The bottom line is that a blog or an LJ is a reflection of the person doing it. Unless you're a hardcore political junkie