BookCrossing is a social service for the literary minded, wherein you tag your books, trade them with other users and then track where they go in the world. There’s no rhyme or reason to how you share a book — give it to a friend, leave it on a park bench for a stranger, mail it to someone on the site looking to read the book you want to share, etc. — and the fun then becomes what happens next.
I haven’t decided whether or not I will join, but I do have hundreds, possibly close to a thousand, of books just sitting in rubber maids. The thought of sending them into the wild to impact another’s life as they did mine is pretty alluring.