Allow me to also posit this:

For the vast majority of social network users, if not all of them, the act of accumulating friends from scratch, trolling through friend lists to find friends and potential friends, and building up one’s own profile page to reflect who you are in this new network, is the primary thing they really enjoy about the social network in the first place.

Put simply, if you make migrating to a new network as easy as pressing a button, you will remove everything that is fun about social networking in the first place. Nobody, including the people who said they wanted the portability, will want to do it.

This whole “portable social network” idea is a fool’s errand that profoundly misunderstands the Web-based social networking phenomenon. It’s a cure that will kill the patient. Which is why none of them will ever listen to the complainers.

On the other hand, though, making the social graph part of a PIM or an Address Book is an interesting and promising idea. Don’t include the social networking platforms at all.