A similar, but more advanced, version of putting a message in a bottle is demonstrated in one of PBS's self-promotion commercials. It shows a woman putting a disposable camera in a plastic bag and attaching a letter to it that says "Take picture and return." She then ties the bag to a balloon and lets it go out into the air. Inside there's a map on the wall on which she's put pictures that she's received from around the world--little African children out in the savannah, etc. I don't see how this would be a very feasible operation, but it's a fascinating idea.