I work in a printing company so i'm kind of biased here.
A book won't run out of batteries.
I can underline passages in a book without having to wash the screen off. Can also say the same with handwriting notes next to the text (e.g. adjusting ingredients or quantities of a recipe in a cookbook)
I can photocopy information out of a book at a library (pending copyright of course)
Can throw a book across the room and it won't break (might break something in its path though)
Can roll up a magazine and smack naughty kids or pets with them. Smacking a bad dog with an ipad might be a touch much.
in all seriousness, reading things on any computer was meant to be the end of books years ago. Nowadays a lot of software is shipped without printed manuals but, in many bookshops, there are printed manuals for that software – Real World Adobe InDesign CS4 is a great example. I think it says something about the help available electronically with the software…
In my workplace if manuals are misplaced/lost/stolen/not there to begin with, i'll find the manual by hook or by crook online and keep it on my HD, but if i need to consult that manual for whatever reason i'll usually print out the relevant pages i need. I couldn't see using something like Kindle or an iphone/ipad for this purpose.
Admittedly i don't read a lot of non-fiction, but it would be good to hear opinions from avid harry potter readers etc as to whether they'd prefer to read that as a printed book or on a kindle or other e-reader.
I do see the advantage for students using e-readers for text books though. I remember back in the day having a backpack weighed down with textbooks and having to lug them home day after day. An e-reader would certainly be a better option there.
I might add that my work hasn't had one customer ask about preparing their artwork for e-readers, and we print lots of books.