Anyone currently using iBooks Author or contemplating doing so should go read this article, "Apple’s mind-bogglingly greedy and evil license agreement”, on The Ed Bott Report on www.zdnet.com.
In short, the EULA for iBooks Author says you can’t sell manuscripts that you create in iBooks Author for anything else other than Apple (even if Apple won’t sell your book).
So, all that work you did to format your book for iBooks Author. Nope. Can’t use that file to submit to anything else.