Once you've read a book or are finished with it, what do you do with it? Do you put them on shelves to read later or in storage? Or do you trade them in to a book reseller, like trading in a video game?
I don't buy very many books, so I tend to keep most of mine. Text books when I was in college often got sold back to the college bookstore, when they would take them for a decent price. A few others went to eBay or storage.