While not strictly social, this did use the underlying Shindig code based used for social gadgets. It also allowed for Cooperating Gadgets in the browser via gadgets.pubsub and distributed Prefs system using gadgets.prefs
In fact one of the use cases was 'add the Google Gadget to your container' so your other gadgets could have enhanced functionality. The only thing missing is a user-owned, portable data store. We're seeing a return to this model in ARCS and Fuchsia.