According to the Association of American Publishers, net book sales fell in 2006 .2%. Certain segments were up such as ebooks which increased 24.1%, adult paperbacks 8.5% and adult mass markets 4.6%.
Down were children’s/YA hardcovers (29%); audiobooks (11.7%); and religious books (10.2%). I don’t know whether the audiobooks takes into consideration the downloaded audiobooks or the fiction inspirationals.
Via Shelf Awareness.