I'm always sad to see books discarded; some hoarder instinct in me says that there must be some way to preserve them.
My particular experience with book dumpster diving was when they were cleaning out the office of a former professor at my college, who had been a student of Dijkstra, and had nine binders with photocopies of the EWD archive [1]. I and two other students split up the books, and to this day I have three volumes of faded yellow copies of these papers. Despite the fact that these are all digitized now in some form it's still a chunk of history that I feel privileged to own.