We too have boxes and boxes of books. Some I've wanted to pass on to others, but not just dump them on the local thrift store. I have about a $75 credit at the local used book store.
I like this idea of being able to pass on books to others. The Athens, AL Quizno's Subs has a sign now announcing that they are an official drop off point. This makes it easier for those looking for books.
In the coming weeks I'm taking a couple of business trips and am looking forward to looking for books in other cities.