Rob McGann, over at ClickZ, has a nice article entitled The Blogosphere By the Numbers, with some interesting metrics on blogging (Deeje, Susan, take note!).

My key takeaways (and if you care about search, local search, p2p, social networking, etc, you ought to care about this too, IMO):

- Demographics: According to a study by Perseus, over 50% of bloggers are 13-19 and another 40% are 20-29. This is interesting, as I'd say nearly all of the blogs I read are published by 30+... but perhaps that's because my blogging (and blog reading) is skewed towards professional vs. personal interests.

- Activity: 275K posts a day (or ~11K an hour). Wow.

- Size: 4MM blogs, up from 500K in June 2003, per Technorati (roughly 15K new blogs a day). 6.5MM blogs, per PubSub... big difference there... Perseus projects 10MM blogs by the end of 2004

Of course, what's missing from all of this is the number of 'Feed enabled' (RSS, RDF, Atom, etc) blogs, where Feeds are concentrated (i.e., how do they map to the aforementioned demographics) and how Feed growth is tracking with overall blog growth. While blogs are tremendously interesting... it's the Feeds that truly give this meme its power.