It's been a long time coming, and looking back, we really should have done this years ago. Organic groups now has a stable release!
I've written about running OG at scale
www.gizra.com/blog/microsi...
#Drupal
drupal.org
Organic Groups
Overview Enable users to create and manage their own 'groups'. Each group can have subscribers, and maintains a group home page where subscribers communicate amongst themselves.