I like the idea of pair blogging. Cate and Sacha, seem to be doing it (intentionally or not). One person blogs on a topic he/she's presently thinking about and the other person posts his/her views on the same issue. Well, comments are meant for that, but a blog post seems to give you greater freedom.
PS: I called it pair-blogging. I don't know if it already has a name or if pair-blogging means something else.