I gave my wife a Sony Reader for Christmas after she'd talked about them for some time (she deemed the Kindle "ugly" btw, which is important as anything else for a gadget that's designed to be looked at for hours on end, I guess). Her verdict on the experience? Good, but there's one thing she's surprised to miss most from real books:
It's not just the smell, the texture, the page turning or the better contrast ratios of a real hardcover that you'd expect. She feels disoriented without the constant, tactile feedback of the book's thickness—that unconscious reminder of just how much of the story is left to go (are there really enough pages remaining for Mr. Darcy and Lizzie to work things out??). Sure, there are page numbers on the screen, but it's not the same.
I found her reaction simple and somewhat profound. While this small detail is far from a deal breaker for the Reader (or any other similar device), it's not the sort of issue E Ink will ever be able to address. Of course, if/when our generations make way for children who never know paper, the industry will have solved its problem of a homesick readership.