Stuff Found in Used Books

I recently had occasion to go through all my books - and I have a lot - to sort out the keepers from the space-wasters. I decided I am through with buying used books from those tantalizing stores that are filled from floor to cieling with out-of-print pulp ... and no longer will I pay even a quarter for something I can take out of the library. But one thing I will definitely miss about old books is the treasure you find left inside the pages. Sometimes it's the inscriptions; and sometimes there's something in there that makes you wonder how this book made it to the bargain bin at all. Did someone perhaps die and their books were disposed of with no-one knowing there was a card and photo inside?