Didn't we go down this path with email? We had ISPs running SMTP servers, until consumers voted with their clicks (Hotmail, Gmail) that they'd much prefer a centralized solution and were happy to trade in privacy for a free almost-always-up, for-the-foreseeable-future permanent solution. Isn't that Facebook?
These are not centralized solutions in the way Facebook is. If I use Gmail does that force you to use Gmail?
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 administer the mail for a local ISP, 10k domains.
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.
