Perseus Development Corporation conducted a survey of the weblog landscape. The methodology is not described in any way, but assuming the numbers are correct I'm not sure if they're dire or exciting.
The white paper notes a high level (66%) of abandonment. Basically there's been a lot of tire-kicking going on.
On the other hand, that's 66% of 4.12 million sites. So we're still talking over a million that are regularly maintained. Then again, maintained, here is a very loose term, including blogs that only update about once every two weeks.
Again, interesting numbers, but not enough context to be insightful. For example, what time scale is the study on and how do these numbers compare to the growth of other online communication tools.
I'm guessing answers to some of these questions can be had for a small fee.
Thanks to Scripting News, which has just rediscovered the concept of social capital.