I just wanted to pitch in my two cents. I think Digital Editions is quite nice yet I believe there are a couple of things missing. The GUI could get a little "pimping" so it looks a little more like iBook with the shelves and such, just from an aesthetic point of view. Maybe linking it with a simple, good looking, FAST flash app might work. Also, we should be able to modify the books margins. Many of the books from the Gutenberg Project don't come with margins. Also it would be nice to have a full screen view and perhaps a change of the white background to the more matte beige for less eye strain.
I hope I find some people to echo these proposals so that adobe can incorporate them in future updates.