Oliver Wrede provides a really excellent framework for thinking about weblogs in higher ed in this detailed conference paper.
He begins be emphasising that blogs create a particular form of authorship:
Weblogs are not special because of their technology but because of the practice and authorship they shape. And it is a practice that will require a weblog author to be connected to processes, discourses and communities.
He goes on to specifiy this:
Weblogs combine two oppositional principles: monologue and dialogue. A reaction to a statement is not only directed to the sender but also to unknown readers. Very often the weblogger gets feedback from unexpected source: new relations and contexts emerge. This (assumed) undirected communication developes to an open and involving activity.
Weblogs not only enable interaction with other webloggers, they offer a way to engage in a discoursive exchange with the author’s self (intrapersonal conversation). A weblog becomes an active partner in communication, because it demands consistent criteria for what will be posted to a weblog (and how). This »indirect monologic dialog« of weblogs allow to conduct communicative acts that otherwise would only be possible in very particular circumstances.
The whole paper is really worth a read and I will come back to it.