Matt Mower expounds upon the concept of BlogPlexes, ridiculously easily formed communities centered around blogs. I find much that resonates but the analysis of why communities form somewhat lacking. In particular, getting a community to a self-sustaining configuration is quite difficult as evinced by any number of community dotcom craters. Also, attempting to form communities based upon post topics seems to be seeking too fine a resolution. For all its faults, no one's complained recently that there are too *few* Usenet newsgroups.
This item was reached through RidiculouslyEasyGroupForming which expands upon many of these issues and collects a number of other relevant efforts.