Haven't seen any discussion of this here yet, so I'll bring it up.
http://www.teleread.org/2009/02/06/p...g-goes-mobile/
Project Gutenberg is going to be developing downloadable encapsulated Java apps as a format for its books, so they can be downloaded into cellphones (and not just smartphones either—any phone that can run Java apps).
That's certainly one-upping Google Books, since you have to stay connected to the net to read theirs…