This is my new hangout, a techy geek club blog. The comments on this post are intriguing, as well.
I like the idea of faceted books, in fact I think that's an incredible name for such an animal. Faceted Books. Or even Faceted Content. Nah, too blah.
But anyway, I can think of a ton of things to add to books. Take HINTERLAND, the book I'm currently considering for epubbing myself. I could write features underlaying the narrative, sort of like Director's Commentary, something a reader could turn on or off with a button or version choice. It could be useful for fans or other writers, why I treated something a certain way. Or yanno how some folks love tons of character description, local description...you could write clean version and underlay it with more story information. Other POVs, maybe, imagery, and inspiration. You could add reviews at will, throw in tons of other commentary, add a frickin' comments section at the end of each chapter...
Gahh... it's too much fun to even think of. I'm going back to vacuuming.