I think that's something that each of us has to decide for himself, Bierus. To me, the overriding ethical consideration is to make sure that the author, and yes, the publisher too, get compensated for their various investments plus a reasonable profit.
I've considered doing exactly what you've mentioned, checking a book out from the library, and then reading an ... unofficial e-version of it. I don't have an ethical problem with it, personally.
