BTW, I read for a few hours every day, so I do not consider myself a casual reader at all. I like to keep my content in the cloud, and only keep on my reader the next books on my to be read list, since I can access my cloud library from my device any time, and put it on my reader with the tap of a finger.
Also, since I borrow about 75% of my reading content from libraries (I have 5 library cards now), as soon as I am finished with a book, I return it and remove it from my library.
After reading Boogenhagen's post I'd like to add that Amazon does not offer an easy way to organize large libraries - at all. You need to use Calibre for that, or you have to select the titles one by one.