A Community of Communities?

Has anyone tried using Drupal as a community of communities?

Yahoo Groups is a good example of what I mean. A single user can be a member of many groups (and can create his own groups, for that matter).

I've been using Drupal for quite a while now, but I haven't figured out how to accomplish this. I tried Organic Groups, but I couldn't get it to mimic the simple functionality inherent in Yahoo's system.

My motivation for this is my mother (gotta love her!). She is currently paying ~$30/year for a family website at myfamily.com. Here, people can share news, recipes, events (birthday & anniversary notifications, etc.), and photos, but it is private to their family group. The creator of the group has wide administrative authority in the group he/she creates, but not in other groups that someone else created. In fact, a member cannot see another family's group, unless invited by the group owner!

When I first saw her site, I thought, "Drupal can do all of this!", but now I've run out of options. Obviously Drupal can do many things needed already. The content creation functionality already exists. Commenting on pictures and news can already be done. In fact, most of these things can be done out of the box, or with a contributed module here and there. I can easily see how Drupal can work for a single family's site, but what about groups of family sites?

In concept, it seems easy enough to simply add a variable to each node (taxonomy, maybe), but how can this be done so that it is invisible to the users? Because of their nature, it would be easy to figure out what theme to attach to a specific node, but what about when it comes to module-generated pages?

Is this just a minor change, waiting for the right module, or would this require a fundamental design alteration? Or will the Organic Groups module do this and more, and I just haven't been able to figure it out? It seems as though, if this were easy, it would open an entirely new wave of possibilities for Drupal.

Any ideas?

- Corey