I don't think you need copyright-free access to the whole book. Interesting quotes/passages are few and should be OK to provide under fair use (e.g. seehttp://onlinebooks.library.upenn.edu/fair use-explain.html).
Well, I wasn't limiting it to meme-friendly fragments such as "To be or not to be" from Hamlet. To go back to the premise mentioned by theswan, it was "good college-level literature course".
That means most of the text like Hamlet is discussed and annotated front to back. A literary guide such as Norton Critical edition of Hamlet will have annotations for every single line of the play. Hamlet is easy to digitize into RapGenius because it's 400 years old and public domain.[1],[2]
For a recent book still under copyright such as Twilight or Harry Potter, the rabid fans could conceivably want to discuss every page of the book. Therefore, a thousand fans "sharing annotations" leads to reconstructing the entire book. If the entire book isn't presented by the website to annotate, what exactly would they be annotating?
For literary and difficult books such as Ulysses by James Joyce, the entire book begs to be annotated. If a permissive license doesn't exist to present 100% of book for thousands of professors and students to share annotations, I'm not sure what the value is.
