Don't know if this article has been posted before, but its a fairly broad survey of book earnings and royalties for 4 dozen publishers. If ya haven't seen it, might find it interesting in terms of where your sales fit.
http://www.brendahiatt.com/id2.html
She last updated her survey in 11/09
http://www.brendahiatt.com/id2.html
She last updated her survey in 11/09