You said: "I think it has to be a part of a large _service_." My question was about the size of the _network_. In any event, following your line of thought, d

You said: "I think it has to be a part of a large _service_." My question was about the size of the _network_. In any event, following your line of thought, do you think it's possible to have a many _small_, separate networks that were somehow part of a large service? Regardless of your answer, does our solution have to be a "service"? What if it is a "product" that creates small networks as overlays on a larger, existing network such as the one all your friends are connected to: the internet? You said: "I can see that it's possible to create a service around, say, PGP..." What if you could see that it's possible to create a service (or product, or both) around, say, a scheme that involved only a single shared password and a single shared encryption key? That is, each friend has to remember only two strings for each network to which she belongs, sort of like, say, a username and password. What if you could see that such a scheme might not require logging on and logging out as frequently as a web-based service such as Facebook? Would that change your thoughts at all? You said, when referring to a PKI scheme like PGP: "But I think that [the] level of conceptual overhead is more than lay-people are willing to deal with." I once thought the same thing about Amazon's S3 service. When I saw the Dropbox product, my thoughts changed.