Being able to see my ebooks as books on virtual shelves is the very feature I miss in Calibre a lot. A virtual shelves view, available in quite many ebook managment programs (e.g. http://ebook-lib.com/
) would be a great additon in my opinion.
A simple view of multipile covers and titles (like on the first screenshot at the latter website) would be practical as well. I would love 3D models of books as well (although I guess is just too much of a hassle).
Just giving some ideas