It might be an enlightening experiment to leave a book that you have read in a public location--ie. doctor's office, coffee shop, plane waiting area, and imagine that a fellow book lover will pick it up absolutely thrilled at the thoughtful gift from a stranger. Better yet, tuck a note inside the cover locating its drop-off and ask the person to add to it when they move the book forward.
If you like this sort of thing, then you should check out an organization, Book Crossing www.bookcrossing.com/
Book Crossing encourages readers to read, register, and release books for others to enjoy. It includes a way to track books released, add journal entries and reviews.