There is a small but decent library on deck 2 by the elevators. I'd take exception to the previous post that it is "just awful" unless it has gone downhill a lot in the last year. It has a wide selection of books, most published by Hyperion (a Disney division). There are books about cartooning, history of the Magic, books about Disney personalities, even a knitting book that I looked at on our last trip! I'll admit that it isn't your public library. There was a Disney Princess story book that DD liked...actually, a pretty good assortment of children's books, and also games that you can take to your stateroom. They just ask that you sign a book when you remove something.
The adult section doesn't have any popular reading, mysteries, etc. that I remember....no romance fiction, etc. It really is limited to Hyperion publishing in the adult area.
So, bring along what you want to read, but if you forget, you should be able to find something entertaining. Or maybe, I'm just not too picky.