Short of a holo deck I can't imagine books ever fully being replaced. Books were created centuries ago and even though we have so much technology people still read books. Nothing can replace the feel of a good book in your hands.
I don't think books will ever be totally replaced. I read e-books from time to time and it just isn't the same like many have stated. I love the smell of the pages and the feeling of comfort holding a book. Snuggling up with a book feels like being with an old friend again. Another plus for books is that after looking at computer screens all day at work it is nice to get away from it at home.
The variable in this is the children coming up now. We feel this way because we grew up with actual books. They might not have the same bond formed with books in childhood that we did. There will always be at least a size able minority that read books however. Whether it will only be a minority will be determined in the next 30-40 years.
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One reason books are always better: in times of turmoil books always out last other media forms. Its really hard to get rid of books. If you want to test this out, check out a typical home (Probably yours if its typical) and you will see books all over and for everything from simple instruction manuals to novels, maybe a religious book or two, etc. If you had to collect them all it would be a task! Books seem to find their way into every part of the house and when they are not used they disappear into it only to reappear at a later date. No other media form can do it. With books you don't need a special plugin, view screen or program, you just open it and start! What can beat that?
I can't stand ebooks at all. I'd rather hold paper in my hand and feel the magic flow from it. The smell of paper and how old or new a book is adds to the fun. I feel no magic towards an ebook. Alhough I like audio books. Who doesn't remember their parents reading you a book when you were a kid and it relaxed you.
I think books will still continue to exist in the future but a lot of them are more likely to be replaced with modern technology since some people dislike reading books and prefers a device to get the same information from to make it easier for them.
I say no it has not, though they are becoming less prevalent because of easy access to literature online as well as ebooks. Myself, I will always make sure to purchase a printed copy of a book I truly enjoy.
Sighs, I admit though even I make heavy use of PDF copies of different books, mostly roleplaying. Mainly because it is cheaper and more covenant. Which, I admit, is part of why books may be at risk all things considered.
I think that book SHOPS are going extinct, but not the books themselves. I believe that myself and other people enjoy the sensation of flipping through a book too much to switch completely to eBOOKS, even if they are cheaper. With Amazon and other online distributers though, book stores like Barnes and Noble are dying out. I can purchase a book for $20 in the store, or for $10 online. Unless the physical stores get competitive in their pricing, they will continue to disappear.