For users to have true data portability, there needs to be some consensus on both the APIs and the formats needed to transfer / represent this portable data. It may be that a number of APIs and formats are required for different scenarios. The Semantic Web is an ideal means for representing the data to be ported from social websites, in that is well suited (using vocabularies like SIOC and FOAF) to represent how people and all kinds of objects on these sites are connected together (documents, discussions, meetups, places, interests, media files - whatever). Of course other data formats may be used, but most importantly, it would be a waste of time to come up with a bunch of new formats for representing the data that needs to be portable, because a lot of work has been done on how to best provide interoperable, reusable and linked data through efforts like the Semantic Web, AtomPub and the microformats community.