Something as simple as mandating that all of a user's activity (and with all I mean including e.g. click tracking on FB or external sites) and accessible information (i.e. posts the user can view) can be exported in real time in a machine readable format would basically do the trick.

It'd allow you to basically build your own Facebook app, migrate meaningfully to another service and build other services that meaningfully integrate with Facebook... and effectively turn FB/Twitter into public utilies and enable real competition to Google to appear by allowing users to share key data such as which result they clicked on in response to which query.