Brian and Paul,
In terms of expectations for student writing, teachers correcting, and so on... This discussion is really no different than the "How good does it have to be before we can put it up in front of the school?" discussion teachers have had with themselves, their colleagues, and their students for a long time. But now of course the stakes are higher, with the worldwide audience.
As a third grade teacher (for a long time), I've found myself getting clearer and clearer in my expectations with my kids on their writing, to the point that they are even stated publicly on our blog. See the new "Teacher Assignments" area on our classblogmeister blog at http://roomtwelve.com/ If kids submit something that doesn't measure up, they get behind the scenes specific feedback from me the next time they log in. (just for old times' sake, they see it in red - grin)
There's a helpful and very active classblogmeister group at http://groups.yahoo.com/group/classblogmeister/ I think anybody considering using classblogmeister will find it useful.
Lastly, the critical concern appears to be TIME, right? That's the bottom line that many don't consider when giving advice to classroom teachers. Sure, maintaining a classroom blog for your students takes time. So does teaching writing. We teachers have to be willing (and allowed) to change the way we do things - the way we teach, the way we plan, the way we evaluate, the way we archive work.... Jeff Utecht lays it out pretty clearly, I think, in a recent post: http://www.thethinkingstick.com/?p=583
"It’s really no secret. You have to change the way your class runs, you can not add blogs to what you do, they have to become what you do!"
People like Paul (in the comment that prompted Brian's post) are just naturally asking if the same rules apply in web 2.0 land. For me, it's not that expectations have changed. But the change in audience certainly makes me take a closer look at those expectations. This is a good thing.
The tough part is time, of course. Jeff was exactly right in that we teachers cannot ADD blogging to what we already do. There is not enough time in the school day, nor in a teacher's life to do that. So we have to REPLACE part of our practice with blogging (or wikiwork, Tubing, Twittering, whatever).
These new tools can't be used as add ons. They have to replace existing practices.