I read a book [link] that said that during the 20th century only a tenth of people would actually read all of a book they aquired
If ebooks, as specific reader gadgets, could up that to a third or even two thirds then ebooks would have more purpose
If it actually tripled absorption people or
firms could justify book with reader rather than just book. maybe. (I say maybe as I think retention is different between the two media)
anyway an eBook could sense when you were getting nonattentive at the scrollbar or perhaps even read your pulse
On detecting drifting attention the ebook could suddenly grab a piece of writing that started with one of a few hundred Zing words suggesting that if you kept going you'd get there
The effect would be a little like a magazine with the lively quote or gist appearing as a sidebar
the reason this is actually a fresh feature rather than say an ancient printing tradition is that the Ebook is measuring your reaction to the material with the goal of keeping you reading