Some while ago, I took part in an experiment where the idea was to pass on an email message to reach a randomly selected person (I think my "target" was a Russian university student). The only drawback I can see with this kind of experiment is you'd need to get everyone you know to pass on the message to everyone they know, to be sure you weren't missing a potential link in the chain.

Maybe there should be a folk version of the Kevin Bacon game...