Why this format? Because writing (for me) is a long, painful business, and I don't plan to go Stephen Fry Web2.0 cold turkey. And with the possible exception of Friendfeed and Twitter, Facebook is the place that holds my hand and is most likely to keep me going. Why not another blog? Because I'm writing a book, not a blog, and this format is best suited to microchunked contributions with threaded discussions.
Good idea or not? We'll see.