Nothing like enough. I want a cast-iron guarantee that they will never, ever delete anything from my Kindle under any circumstances. They have absolutely no right to do so, and in fact, I'd go so far as to say I want them to remove any such capability. As has been pointed out endlessly, if I bought a physical book from them, they cannot do anything to it once it is in my possession. There shouldn't be any difference just because it's an eBook.