After looking around for a blogging community for some time, I came across BlogCatalog a while ago - and have been impressed with it.
BlogCatalog started life as a directory of blogs, with widgets to show recent visitors to your own blog - and expanded to include groups, discussions, and the ability “friend” each other in much the same way as the popular social networks (I find myself wondering if they are using Drupal as their back end - these are all things Drupal does well, and integrates well).
The discussion forums are filled with a diverse and active crowd of people - they appear to have passed the critical mass where visitors are self generating purely on the value of the community by its size.
Head on over to blogcatalog.com and take a look!