I once taught a class where there wasn't a "class blog," and each student had his/her own blog (as in this class). But the blogs were all resident within the classroom-- I can't explain it, but you know what I mean. There was a tab for "Blogs," and you clicked on that and there was a page with the thumbnail of each blog. I found there was a lot less contentiousness and a lot more friendliness because-- this is odd-- the students kind of respected each other's "ownership." It was like if you go to Aunt Mary's house, you don't argue with her, where if you were at a restaurant and she said the only true sign of womanhood was childrearing or whatever, you might take issue with it. So if you went to Sarah's blog, you might comment, but you wouldn't object to what she said because, after all, it was her blog.
I don't know if that was good or bad, this "ownership" and courtesy. I've had an editing blog for years, and I have to admit that while I loved getting questions and comments, there was one commenter who constantly disagreed with me. (I mean, the subject of most of the blog posts was "punctuation," but she still managed to disagree about commas. <G>) I think I was a lot more annoyed at her because it was MY blog. (And, to be fair to me, she was generally just WRONG and was pretty obviously disagreeing because she didn't like someone else being an "expert".) I kept wanting to say to her, "Why don't you start your own damn editing blog, and there you can say that introductory elements don't need commas, huh?"
Some Web 2.0 media is "social," but some is still "private ownership." And I bet that dictates to some degree the level of formality or something. Like email is "private" and "mine," which is why we get annoyed with spam-- what is this junk in MY inbox, where we wouldn't worry too much about ads on the Yahoo page, say.
Something to take into consideration. Do we want to encourage "ownership" as an "investment" so we assign "private" Web 2.0 devices? Or do we want more to encourage collaboration, so everything is "joint?"