Rarely a day goes by where somebody doesn't download a copy of Blackmarsh. My sales report show the order number. I then realized that while it can't give an accurate number of sales on the various One Bookshelf sites it may be useful to see what happens year to year.
In addition my own personal orders goes back to January of 2007 (a copy of Castle and Crusades Monsters and Treasures) . So after some fiddling around I came up with this chart from 2007 to 2013.
Wow, 1.2 million order numbers in 2013! Probably a fair amount are cancelled or generated for administrative purposes but that would be true of previous years. I think it safe to say that the volume of sales at RPGNow has nearly doubled over 2010, and nearly four times that of 2007.
I suspect most of the post 2009 increase tracks the adoption of various tablet devices.
Anyway it food for thought.