figures from the Association of American Publishers shows drop in sales - September 2011 compared with September 2010

This is clearly a worrying set of statistics - the 100% increase in e-book sales doesn't compensate for drops in other categories, and the total trade was down 6.5%.  It must be assumed that the buyers of "adult mass market" (paperbacks) represent the bulk of the increase in e-book sales. Association of American Publishers website