I will have nothing to do with app-locked ebooks.
(Non-negotiable)
That means no ebooks I can't get as standalone files.
I can tolerate password protected files so long as I know the key. Hide the key and I'm gone.
Back in the day I bought DRM-free and LIT.
When Mobi was cracked, I added it to the approved list.
When Fictionwise went away, I switched to Kindle for the few encrypted ebooks I buy.
I don't upload or share except to my mother, whose Kindle is tied to my account anyway, so watermark DRM doesn't bother me. I just want to move my books from device to device as appropriate and/or necessary.
But that is me. I reread with some frequency and I switch toys from time to time.
I can understand that people who do neither can be and very often are quite happy using encrypted DRM systems that are account locked (as opposed to device or app-locked). It is all a matter of being able to use the product in a reasonable fashion without the DRM getting in the way.
For example, I have no problem with the DRM terms for digital downloads on the XBOX 360: hardware-tied to the console you first buy it on (or assign the license to) so anybody can access it on that device *plus* it is also tied to the account of the buyer so it can be used on any device where that account is active, so it can be downloaded and used on other consoles. The combination covers 99.9% of usage scenarios so you rarely if ever notice the content is DRM'ed. Of course, just because I'm comfortable with the terms doesn't mean I don't prefer to buy the disk version whenever the price is comparable.
I don't see it as a "matter of principle"--producers are entitled to make a living--but I won't give money to anybody who gets in the way of my specific needs. It's my money and I won't settle for anything less.