A related concern: 1984-style "party" that views any historical content as a threat to it's existence easily censors and edits both non-fiction and fiction literature to promote itself.
With paper printing and thousands of independent copies, this becomes difficult. With digital copies, especially in an iTunes-match or Amazon Digital Locker scenario, this becomes trivial.
If you think this is paranoid, watch the latest moves that DHS and TSA are making and combine them with SOPA for chilling effect.
The digitization of books is, to me, like the digitization of voting - appealing, but very dangerous and possibly not worth the societal dangers that come with it.