Mind you, I love my Kindle, and my relations with Amazon customer support have been uniformly excellent. But they hold the keys - that's what you agree to when you read their terms of service. So anything I really care about, I have a dead-tree version.
AND they can orwellian alter books for the PC moment de jour.
Additionally, people are coming to realize that their “library” of digital books, albums, and movies cannot be given to anyone else when you die.