Eric — I think you’re right to teach blogging as a way to think about audience and purpose and all of those things. I use blogs for those reasons, too. But I think teaching blogging as a skill of its own has value, and lots of it, for the reasons that Connie mentions in her comment.
Bonnie — I’d recommend checking out, an Elgg set up by Worldbridges. It’s for folks who want to dabble as well as communicate with other educators.