How many blogs are there, anyhow? Sébastien Paquet has been collecting information on the topic: Weblogs By The Numbers.
Interesting topic...and perhaps an interesting graduate project topic for one of my students, too.
There are really two questions...one is how many bloggers, the other is how many blogs. People like Joi Ito are using multiple tools...he uses Movable Type, Radio Userland, and LiveJournal, along FotoLog and other tools. So he counts as one blogger, but with four or five blogs.
The "how many bloggers" almost has to be done with survey research. The how many blogs may well be doable technically, but it will need a lot of work. (If it were easy, TechnoRati wouldn't keep showing all of my archive pages as separate blogs pointing to me...)
Updated, 12/17
Interview with Cameron Marlow, creator of Blogdex and researcher at MIT Media Lab.
Right now Blogdex is crawling about 16,500 weblogs. This number has been as high as 22,000 and as low as 12,000 (when the index started). While there may have been 1.6 million weblogs created in the past 3 years, only a small percentage of those are still active, and an even smaller number are updated frequently.
It might be worthwhile to ask for a couple of questions worth of a rider on the Pew Internet & American Life telephone surveys. As I recall, they were planning on doing something in this direction. This wouldn't help our North-of-the-Border friend much, but it would provide some sort of a growth statistic.
Hey, Liz, do you mind taking a look at this? I really want to be a part of blogresearch, and maybe this could be my contribution:
http://www.tc.umn.edu/~ratl0016/GenderBlogging.htm
I'll post it over there (blogresearch) too.
You may be interested in http://blogcount.com, where I report studies, stats, surveys, censuses on the size and shape of the blogosphere. Send suggestions to tips@dijest.com, please. - phil