i think these are all valid questions and you're right to be thinking about them. they've been discussed here before, and surely will be again... there is not really a black and white answer so far, i think, since people tend to amalgamate these questions with copyright infringement questions and both ethically and legally opinions diverge quite radically sometimes.
personally, i consider format shifting to fall under fair use (that is, if i have a cd, and i want to listen to it on my mp3 player, then i see no harm in ripping it to do just that). given that, if i've bought a book in paper which i would like to have in digital format, i think it would be perfectly reasonably to scan the book and create an e version. now, where the arguments tend to get rather more tortuous, is whether this can be extended to downloading a book instead of spending the time and effort to make the scan yourself. personally, i tend to believe it can, *particularly* so if the book is not available as an ebook, which is the case for many many books. others disagree, and feel that if you want the same content in a different format, you should pay for it twice.
for the moment, i think it really comes down to what you can legally do in whatever country you live in and also what you consider to be morally acceptable. i hope that when ebooks start to become more mainstream, we'll find satisfactory answers to all these questions (which hopefully will include the availability of all titles as ebooks).
there have been a few threads recently discussing the difference between
content and container, and discussing possible new models for the publishing industry. i'll see if i can dig them up.