Great services like Gmail only became possible because SMTP isn't tied to a particular proprietary service. Individuals can use the service that's most appropriate for them. For some people, that's Outlook, for others, a webmail provider. Competition works.

What we really need is a system that crosses social-networking-service providers in the same way that SMTP broke down the barriers between various mail systems.

I think the idea of a Balkanised Facebook is a good one, esp. if was business related. Keeping in touch with customers and aligned groups in a relaxed place but without the threat of one of your personal friends posting pictures of what you did on your drunken weekend away.