This just in:
MySpace is going to allow users to share information from their site.
This is definitely a step in the right direction, but notice that sharing is done either by copying/synching, or through their specific APIs. It doesn't fully extract the content into a separate layer with application-provider-agnostic service APIs.
One can imagine an OpenSocial API on top of a social network data service that is used by numerous providers but owned by none.