Social Reading?
Amazon's Kindle app for the iPhone and iPod Touch has recently introduced a feature that highlights sections of a book and if you touch the highlighted text it would tell you how many others have also highlighted that part of the book.
I see tremendous value in this. I would love to 'share' sections I highlight with a selected group of people. Currently it just shows the count of all other users who also highlighted the same thing. You don't quite get the "social reading" aspect but you get an early sneak peak of where this is going.
Now this section in the photo above is, ironically enough, from a book called "Empire of Illusion: The End of Literacy and the Triumph of Spectacle