This is when dumpster diving pays off! I picked up a stack of very old books from the garbage. They must not have been in there long, as they were still very near the top.
I gave an old medical book that was in the pile to a friend who is a nurse practitioner. Another was a very early 1900s copy of House of the Seven Gables which still had a handwritten homework paper in it from the 1920's. Another was a youth's book from the 1870's. Some little kid wrote a letter to Roy Rogers inside of the cover which is quite a mystery as to why.
Finally, the book Old Christmas. I did a little research on it, and found it to be a first edition of the first American printing! And, while it does have value, I fell in love with the book, and it will go on my shelf.
I'll add that, when I saw the pile of old books, I just scooped them up and looked at them later in the day. As I love old books, when I see them being discarded, I just grab them, knowing what I don't want, friends and family will.
With this pile, it was none too soon, however, as not 5 minutes after I grabbed them, the skies let loose and it poured. Only a few minutes later, and these books would have been soaked and lost!