My friend and colleague Paul Chaney is working on a blogging book with another author and recently asked for some advice on schedules and how to work on a multi-author book. I responded and thought it would be interesting to pull the response here into the public eye too…
“The book is scheduled for release in the fall and they want a completed manuscript by the end of March. Not having had this experience I have no clue as to whether that’s a reasonable time frame, but we aim to please.”
First off, congratulations! There’s little as satisfying as publishing a book and bumping into people who have read it!
Having said that, I do believe that a perfect egalitarian coauthorship doesn’t work and that there needs to be a lead writer whose voice ends up permeating the entire manuscript. That’s what Shel did with Naked Conversations, for example.
You need to balance the rewrites and work, of course, so it’s still equitable, but books that are collections of essays, for example, are always spotty and plagued by bad writing, making it hard to find the gems.
Further, I would assume that each chapter is going to go back and forth between coauthors at least twice. You brainstorm points and cases, your coauthor adds to it, you write a first draft, they add their content, you polish and send it in. (Or vice versa).
Once you’ve sent in the manuscript, remember that you’re both part of a bigger team of editorial folk and that you’ll have AT LEAST two or three more people adding their 2-3 cents worth, including a tech editor , copyeditor, and development editor. Value all their comments (it’s easy to get mad at them) and respond to each query with the question of “they represent the reader. How can I improve this for the reader?” rather than the more common, but wrong-headed “stupid editor. What do they know about this subject?”
Finally, once it’s all done, remember that’s when your work STARTS, not ends. Successful books are a success because the author(s) push them, not beacuse the company gets behind them. Most publishing companies assume everything will be mediocre and only put marketing $$ behind those books that are starting to demonstrate the traits of a success.
One implication: be extremely generous with review copies. Any visibility in your market segment makes it easier to get more marketing attention and, of course, is good for your book sales overall 
Hope this is helpful stuff!
 I do tech editing of books, particularly those with a business focus if anyone’s interested, and have tech edited at least 30 books in the last decade. It’s fun and a nice chance to help improve a product. [References]
 And this is why if any one of you would like a review copy of my nineteenth book, Growing Your Business with Google, and have a legitimate outlet for a review, even just on your well-read weblog, please contact me and I’ll forward your request along to the publicists at Penguin. I’ve sent out at least 50 copies of the book to reviewers at this point in time.
by this point in time…