Matt Gemmell:
As with any publishing workflow, you will want to do the writing and editing first, and then put the book together (as much as possible). iBooks Author is resolutely not a writing environment.
It will be an interesting exercise to do this when (if) my book ever gets finished.
Tries to read 1 book a week, listens to music at work and podcasts on the train, watches quality TV to unwind and owns an Xbox 360.