The Blogging of the President: 2004 brings us The New AP: Atrios versus Instapundit, Part One. I think he's on to something. Certain blogs, like Atrios now serve an agenda setting function that is filtered through the traditional media to the public.
The article also has some interesting things to say about the contrast between Atrios and Instapundit, described as a leading agenda-setter on the right (which I hope is not right, as it would be sad for the right).
That said, the guys who really matter are the ones who come up with the facts, folks like Brad DeLong or Josh Marshall.
*Blush*
Don’t be so modest Brad, your job has done a spectacular job at getting people to think about economic issues more clearly, rather than responding to numbers as factoids to be reacted to. Call it one of the unlikely stories of 2003: how a Harvard trained Berkeley economist became one of the most influential people on the net talking about the details of productivity, employment and exchange rates.