CJR Daily has an item about a study by Harvard's Joan Shorenstein Center on the Press, Politics and Public Policy called Creative Destruction: An Exploratory Look at News on the Internet.

Here's one finding (from the report's executive summary):

The websites of national “brand-name” newspapers are growing, whereas those of many local papers are not. The sites of national “brand-name” television networks are also experiencing increased traffic, as are those of local television and radio stations. However, sites connected to traditional news organizations are growing more slowly than those of the major nontraditional news disseminators, including aggregators, bloggers, and search engines and service providers.

The study looked at eight prominent blogs. CJR said the only clearly right-wing one amongst the bunch was Little Green Footballs. Those blogs showed only six per cent growth. National newspaper websites went up 10 per cent, and national broadcast sites went up 30 per cent. Aggregators like Digg and Topix showed "explosive" growth, but those are very new forms and so they started with a base of almost nothing.

CJR's Paul McLeary made the following observation:

Another thing that probably led to the smaller growth percentage among the political blogs--especially the highly partisan ones the study looks at--as compared to big newspapers, is that the sample set has probably come pretty close to maxing out on its potential audience. There are only so many hardcore political junkies out there on either side who want to read what these outlets have to say. It's by definition a niche audience, and as such its growth, if it happens at all, will probably be slower than that of a general-interest newspaper.