I missed this from biz school prof Kevin Dooley back in August, 2008:

[H]ow are polit­ical blogs the same or dif­fer­ent from MSM? Through Wonko­sphere, we have noticed that polit­ical blogs are con­sumed in much the same man­ner as main­stream media is, which indic­ates that read­ers treat polit­ical blogs not as sep­ar­ate from, but rather as part of, main­stream media. Wonko­sphere traffic is greatest on Monday, and tends to peak before break­fast, lunch and din­ner, i.e. when people are cruis­ing on the net to end a por­tion of their work day. Blogs act as news­pa­pers for most.

Second, very few blogs break stor­ies. From our data, the vast major­ity of blog­gers still rely on main­stream media for the con­tent they com­ment on. In fact, a blog­ger is just as likely to cite main­stream media as they are another blog­ger. Thus, blog­gers are primar­ily amp­li­fi­ers rather than sources of news.

Third, the pop­ular­ity of polit­ical blogs tends to fol­low a Pareto (power) law, mean­ing that there are a few blogs that have hun­dreds of thou­sands of read­ers while most blogs only have a hand­ful of read­ers. This means that the influ­ence of blogs is dis­trib­uted in the same way, lead­ing to the devel­op­ment of élite blogs (MyDD, Town­hall), in the same way we have élite main­stream media sources (New York Times, Newsweek).

Put together, these pat­terns imply that polit­ical blogs are act­ing as sup­ple­ments to main­stream media, rather than sub­sti­tutes for it. Their impact on the sys­tem is to increase volat­il­ity: blogs make most news spread faster, but some­times they slow it down. Blogs spread fact, opin­ion, truth, and slander more rap­idly — it is not biased in that regard. Only a few blogs influ­ence opin­ion most of the time, but any single blog has the poten­tial to impact everyone.