To blog is to keep a weblog or, specifically, to post something to that weblog (as in pressing the "BlogThis!" button that comes with the Blogger publishing tool, one of the more common weblog tools in use).
Blogging about blogging
I've rarely seen any genre, medium or format featuring so much meta discussion as do a lot of weblogs. Questions like "Why do we blog?" are repeatedly asked and answered, outlines for ethics, manifestos and guidelines for blogging are made and commented on, what makes their way of publishing different from that of the more traditional media is discussed. Etcetera. And then some. Why is this?
The blog is a young medium. Yes, I think it is a medium or, perhaps, a format, weblogs are far too diverse in content to be called a genre in my opinion. There are actually blog novels, for crying out loud, even if the majority of weblogs look more like surf reports, news commentary, me-columns or diaries. Calling the blog a genre makes about as much sense as saying the book constitutes one. It's a medium, and a rather young one - Tim Berners-Lee is credited as having made the first weblog in the web's pure infancy, but the whole thing seriously took off only a couple of years ago, with the introduction of easy-to-use weblog tools and free bloghosting services.
Also, weblogs are no doubt read by many sorts of people, but what seems certain, is that they are read by other webloggers. This is seen in the blogrolling lists appearing in the left or right column of most weblogs, featuring the weblogs the blogger reads more or less regularly. And it is of course seen in the frequent cross-linking and debating between weblogs.
Corporate weblogs exist, so do weblogs that are part of established publications, such as Dan Gillmor's eJournal. Most weblogs, however, are published by individuals of little RL fame and with limited possibilities of marketing. They need to get noticed by other weblogs, to become a recognized part of the Blogosphere, and their safest bet for an MO is looking at what the others do - what makes for a popular weblog.
Also, bloggers are often people of strong opinions, opinions that might, politically, diverge to the extreme (from the libertarian-pundit bloggers who want to punch Robert Fisk on the nose to the leftist bloggers who sport semi-communist symbols on their websites, etc.) - so that one of the things they all have in common is figuring out what to do with this still rather fresh medium that they are trying to make their own.
So blogging is expressing yourself through a young medium which holds very few guidelines, with no marketing budget, no real establishment to tell you how to do it except the role models to be found in the politically diverse blogosphere*, and doing so to an audience of an unknown size and demographic, where you know quite a few are likely to be bloggers themselves. Is it any wonder there's a lot of blogging about blogging?
* Some will claim that although diverse, the blogosphere is severely biased politically, but this is not my point here.
See also: Noding about noding | 
