elearningpost points to a "longish" paper by James Farmer. Communication dynamics: Discussion boards, weblogs and the development of communities of inquiry in online learning environments
The discussion board is the ubiquitous communication tool within these OLEs and hence significantly shapes the kind of communication that takes place. In light of this, the degree to which a successful community of inquiry can be facilitated through the use of discussion boards is examined and compared to the possibilities afforded by weblogs in the same role. Weblogs, it is argued, offer new opportunities in the development of social, cognitive and teacher presence online and should be considered in the development of or alongside established OLEs.
And from the conclusion:
Under similar examination, weblog technology can be theoretically seen to more effectively meet the needs of educators seeking to establish a community inquiry online. Consequently, while discussion boards may have a role to play in the shaping of future OLEs it is arguable that this role should be complemented by the implementation, within or alongside these systems, of weblogging functionality.
It's nice to see some well researched perspectives on a subject I've been considering lately, albeit focused on learning environments.