iBooks Isn’t Backed Up
As I’ve said, books can arrive on the device in ways that songs can’t. Suppose a book arrives via Dropbox or Safari on the device, and I transfer it to iBooks. Unless I take measures independently to make a separate backup, that may well be my only copy of the book. And such measures may not be easy to take, because the device, with respect to this strange music-and-movies-and-books category, is like a diode: current passes only one way. Just as you can copy music onto the device but you can’t copy it off again, so too you can get books onto the device but you can’t copy them off again. Meanwhile, the book isn’t being backed up to my computer — and it won’t survive migration to the next-generation device.
I mostly use GoodReader and the Kindle app, but I guess I should be careful with ePubs in iBooks.