I had seen Clay Shirky's recent post, The Seven Two Pieces Social Software Must Have, and was again prodded by Matthew Phillips' comment to put down my thoughts on this.
I think we can easily agree that Drupal supports these two pieces: groups and conversations/shared awareness. But it's not immediately obvious how groups are supported. I have two thoughts on this.
It's been said before than instead of YASN, in the future we'll have our own social networking sites (repeat after me: social networking is a feature, not a business model). And I think Drupal is well on it's way to filling this function. Each Drupal site is analogous to a group. I'm a "member" of the Drupal.org group, I'm a member of the Urban Vancouver group, and of course a member of Bryght (not to mention the personal sites of a half dozen friends). With the distributed authentication that's possible between Drupal sites, I can participate in all these groups with a single login.
My second thought on groups in Drupal is through the use of roles. Today, these are used mainly for applying permissions and access control. But with the 4.5 release, multiple roles per user are supported. This sets the foundation for group-based access and content. It will be interesting to see how the ever-resourceful and innovative Drupal community makes use of this to add even more useful functionality.
There's probably much more to be said on Shirky's post, especially with respect to how I would define the technological signature of Drupal-powered sites, but I'll leave that for another post.