Yes my two books are currently on the iBooks store. And have been there pretty much since iBooks authors was launched. And both of them are doing quite well!
http://itunes.apple.com/us/book/wacky-world-peafowl-volume/id532559767?
In fact, we have two planned to be launched on the iTunes Store in the few weeks. Also, I have two more in the works before summer is done.
However, since most of my photography is done about beautiful Peacocks, I get hundreds of requests wanting a table top book with beautiful peacock photographs like we have shot since the early 1980s.
Until now printing small quantities of a color table top books has been cost prohibitive. However trying to make a profit and still keep the price cheap is an issue with using this service.
I would be remiss here if I didn't remind everyone that Aperture is a professional product for all of us professional photographers and they are providing us with a professional service they would give us a discount for ordering products and quantities.
When I order professional prints from various color labs we have different price than if I was to go to a box store and buy prints from them. And of course the qualities is hundred times better than the box stores.
I have yet to order a sample book for myself but I'm sure the printing job and the quality of the book is second to none since Apple does such a great job with everything that they do.