Apple posts iBooks Author instructional video
The video goes over some of the default templates Apple has included, as well as some of the more fluid user-interface elements like drag-and-drop, widgets and deep customization options. One thing I noticed was the built-in accessibility options Apple has included, which makes creating books that people with disabilities can read and experience much easier. You can also preview your book on the iPad to make sure it looks just the way you want it to look.
All in all, the video is very educational and goes over most of the functionality included in iBooks Author. Check it out!