One aspect to this is how a mass exodus / conversion to a new distributed platform could work.

A web-based tool could be developed that lots of geeks could install on their servers that would allow a person to export their Facebook data into this new service using the Facebook Graph API. Facebook would try to shut this down, so it would have be to have installed and operating in so many different places that they couldn't keep up. And the cool part is that as Facebook tries to shut it down, it will just build more and more media attention, driving more people to leave.

Brand it as The Facebook Exodus, or something like that, set a launch date, and then build momentum from there.