In my line of work I get asked about the future of books with some regularity. I've got a canned, slightly jokey response by this point, but one thing I point out is that the UI of a book is really very good. Part of it is that we've got a lifetime of experience interacting with it from a very young age, but books can be browsed easily, annotated, and scanned quickly. They have an excellent screen and are easy on the eyes and are quite responsive (generally slow load times in regular use). The search is lacking, but there are generally adequate workarounds for that.