See http://blogdex.media.mit.edu/ for a project that uses "the timeliness of Weblogs to find important and interesting content on the Web." <>< tbc
They are very "flavor-of-the-month" right now, in some circles. Those I know who keep up with the latest online fashions are enthusing about them right now. In the context of an encyclopedia article, though, the phrase doesn't seem to have lasting value--over time, it will either fade away or become mundane.
Perhaps, but is that really a reason to exclude something from the Wikpedia? Why not develop articles in real time, as cultural topics develop? <>< tbc
My point is not to exclude the article, but to point out how ephemeral the specific, non-NeutralPointOfView, phrase "very popular" is. If one wants to say, perhaps, "blogs were very popular throughout much of the year 2001" that would be more timelessly true.