Originally Posted by Hitch
Yes. If you've read the whitepapers on digital watermarking, as I have, seeking just such a solution, to satisfy those clients who want some type of protection for their IP, but do not want to interfere with their clients' ability to move a book from device to device, etc., it's not easy to do, firstly (well nigh impossible), and the "casual theft" phenomenon rate is shockingly high.
And this is one common reason that I hear for adding DRM in the first place, not to hinder mass copying from torrent sites, but to lessen "casual copying" to friends and family. The hardcore pirates will *always* find a copy on the darknet, but most people are honest and wouldn't do that. They might have no qualms about casual lending, however, especially if there were no technical safeguards in place to hinder them. All this does, as you state, constitute a significant amount of copying that might have been additional sales instead.
An interesting issue is that if John Doe pays more for a file than for a paperback (which might have a higher perceived value) he might reasonably expect to be able to do at least as much with it as with the paperback. You could call everyone and his grandmother "thieves" and try to prosecute them, but if this does not fit with the public conception of what reasonable uses for your purchases are you have a very real PR problem on your hands.
This is certainly a thorny problem, and no-one has a solution which would satisfy all parties as far as I know.
And - <slashdot>it's not "theft", it's copyright infringement