It seems to be that many people who want data portability are either not representative of the general population or have agendas involving trying to get as many people as possible onto their site.
This isn’t just a privacy concern: I continue to think that the difference in context between different social applications is a key constraint that people are missing.
I’m increasingly of the view that moving contacts from one application to another should require both parties to agree that that they want to be visible to each other in the new context. It isn’t clear to me that this a viable process, though.
(Something that should be obvious but apparently isn’t: portable APIs for web based social application – ie OpenSocial – are extremely good. Moving of personal data – ie, data portability – is something I think still is questionable)