I agree that redefinable key bindings would be a big help.
The thing that I really want, though, is an option for smaller line spacing. The current spacing gives far too few lines per page, particularly with the larger font sizes. None of the devices that use MobiPocket's Java Reader have user selectable line spacing (so this is MobiPocket's fault). Perhaps Amazon could just make the line spacing smaller by default, without making it user selectable.