Fbone - as an avid library user, I really appreciate all the work you put in to this!
One more wrinkle to add to the picture - books with multiple copies may artificially skew the results. For example, the Seattle library has 30 ePUB copies of The Girl with the Dragon Tattoo. Earlier today 23 of them were checked out, so even though over 75% of the copies were checked out, it still goes on the list as not checked out. I understand completely that your numbers are just rough estimates, but I still thought this was worth mentioning.
Thanks again for all your efforts!