We've already got several new tags that have cropped up. Let's pick one and go with it. I think the term portals (taken from Introduce sub-communities (or “Portals”) to prevent fragmentation) sounds the best. It seems to reflect the fact that it's just a subset of Stack Overflow, while "mini-site" feels like an unconnected entity, at least to me. If you have other ideas, suggest them below, or perhaps someone from the team will declare a preferred term. Either way, let's come to a consensus before everyone goes off in different directions.
There's also a lot of people using facebook without any of the previously mentioned tags, so some organizing may be necessary there as well.