bonus: do not leave them in such completely open and random places but rather in geocaches. you are much, much more likely to have good results since the audience is already in tune to this sort of thing.

great use for those skanky little 8mb, 32mb cards that come with most cameras.

non-k-ted:
why go to niagara falls when you could read about it? why make love when you could watch porn? life is slightly more interesting when you actually participate. also, this has a distinctly local flavor and emphasis. and this gives a specific focus.