The Chronicle of Higher Ed has a forum with the thread Following Blogs as a Teaching Tool–Tips?
It has some good ideas.
I especially liked:
Also, instructors really ought not require students to violate blog culture, the standard advice (as for these fora) to lurk for a while before entering the fray. So, perhaps students could, for the first part of the semester, print out actual blog posts that they find, and their proposed, “practice” comments, and analyses of the culture of the blogs (are commenters expected to provide evidence for their statements? is the blog’s audience fairly forgiving of writing errors or is it populated by grammar cops? etc.). Student could posting all of this — actual blog post, practice comment, analysis — on a class blog weekly (or turn inall in on paper) for critiquing by the instructor and classmates.
This is a good idea and would be particularly useful for a class in which students have different majors.