Interesting that you mention PDAs. I definitely fall into the 'book over screen' camp, but there are several books that I have read on my PDA, that I don't think I would have read otherwise. Sure, books are portable, but PDAs even more so. I always have my PDA/Phone with me. So when I suddenly find myself in the doctor's office, or waiting for a ride, or whatever, I whip out my PDA, read a few screens of three musketeers, or Dracula, or Princess of Mars, and sooner or later I find that I've read the entire book.
I think Chimera has hit the nail on the head. We will always have books. They will never go away, but I think folks will move more and more to reading things on screens. RSS technology, better screen readability, longer lasting batteries, less juice required will make portable reading devices more and more attractive.
Project Gutenberg has 19,000 books available. If you could get all of those on one device... I think some reading would happen.