Would you use a cryptographically secure social network?
Obviously, this wouldn't be your "find an old friend" or "find people with similar interests" type of network. It would have one purpose and one purpose only: to allow you to communicate easily and securely with those you trust.
Assuming this sounds good, would you prefer to: 1. Use the service via a web-app (less secure, since it requires that you entrust your password/private key to a third party) 2. Use an open-source thick client or browser plugin (you maintain complete security).
The technology is definitely tricky, and it'd be difficult or impossible to monetize. But do you think it's worth researching/prototyping? It actually seems like one of the few remaining innovations in the social network space.