Another thing we lose with digital books is serendipity. Erin McKean talked about this amongst other things in her brilliant TED talk: https://www.youtube.com/watch?v=J4VzuWmN8zY.
I got a kindle 7 months ago and I was given a regular physical book to read this Christmas. I don't know if it's just me but I found it really hard to go back to the book format. Just holding it is much more of hassle. I also love how I can instantly go to the dictionary on my kindle, which also has the serendipity factor! It's not unusual to hop around from word to word on the definitions of the previous one or just finding words which are above or bellow the word I'm looking at! So maybe that serendipity factor isn't all lost after all.
I'd say something akin to shuffle on an e-reader containing 500 books would approach serendipity.