Books Need Hyperlinks.
Online browsing habits affect the way we behave in the real world - no surprise there. But here's a new one for me - reading a book that referred me to "the earlier example from Chapter 9".
So, to fulfill my reading experience, I first had to find Chapter 9 (not as easy as you'd think) and then flick through all the pages to locate the reference. In the past that may have been acceptable, but today I want to be pointed to the page.
User expectations are constantly evolving, so must the experience you provide.