John Quiggin at Crooked Timber does some interesting sums in trying to work out How big is the blogosphere ?
There are heaps of dead blogs out there (thanks to changes in technology, hosting problems and so on, I’m already on my fourth). I prefer to start with another Technorati estimate, that there are about 275,000 posts daily. If you suppose (fairly arbitrarily, but consistent with the Pew data) that the average active blog has one post every three days, that would make around 800 000 blogs.
Another way of looking at things is to consider the labour input going into blogs. If you suppose that the average blog post takes an hour to prepare (this includes overheads like research, if any, site maintenance, responses to comments and so on), 275,000 posts per day amounts to about 100 million hours per year, equivalent to the work of around 50 000 full-time, full year workers. As a comparison, the US Bureau of Labor Statistics reports that news analysts, reporters, and correspondents held about 66,000 jobs in 2002.
One of the comments makes the key point that readers are also an important part of the blogsphere