Successful blog communities

The Seattle blog portal sparked some reflections about what makes a metablog successful.
Seattle’s blog portal, and the Austin metablog, come out of existing communities. People want to read other people’s posts.
The TopicExchange for the Clickz Jupitermedia Weblog in Business Conference was successful at gathering posts from the conference. I remember the aggregator for Kevin Werbach’s Supernova conference last year was excellent, too.
They were successful because there was a community of people, in the room and outside of the room, who wanted to follow people’s takes on the conference.
Thought that the Sam Ruby wiki should have a trackback aggregator; looks like TimA may have got to it already.
Communication patterns:
* A real-time event with people following in-person and remotely, or
* An active project, where people are working individually and together, or
* An ongoing community, where people are blogging individually and want to stay in touch