Student Blogging

I enjoyed reading 20 reasons why students should blog and I agree with the statement that, "blogging is such a powerful learning material and students should blog."  Some of my favorite reasons for student blogging are that blogging allows students to write for an authentic audience, gives them a motivation for reading, and fosters student-led professional development.  I like the idea of letting students choose the topics for their posts.  Does anyone have any additional justifications for using blogs in the classroom?  Has anyone used a blog for a digital portfolio?