To clarify social integration directions, I have written Communities: synergy with Social Platforms
I'm definitely still in the process of delivering the first 2:
... and in design mode for the last 3.
I mostly focus on Twitter, Linkedin, Google+ and Facebook.
It was nice to see SCN featured in your post!
SCN has a similiar focus. We also recently enabled social sign on with Twitter and Facebook. Please see my post Social Sign On is Here for details. We'll be adding LinkedIn and Google+ soon.