There was a great deal of hullabaloo created on the book arts listserv by the keynote speaker's definition of a book at the Tools of Change conference. In the Publisher's Weekly article, Stein, the speaker, says that the text "scribbled in a bound book or as a comment posted online to a digital text" make the scribbler or the commenter an equal with the author.
As a scribbler in many books of poetry and short prose (probably other things too), I would disagree with the first part of his thesis. I don't consider myself to have an equal role in the text to the author. My scribbling is a reaction to what the author is saying. I'm in agreement, or disagreement, or it made me think of something else, etc.
A comment posted online is different though. As the author, maybe she can react to the comment, and the person posting the comment can have an active role in the creation of the text. Who knows? Maybe the author will just say, "Aah, this is bullshit," and go back to her typewriter and write the next great american novel.