Unlike Erik, I don't think an open alternative to Facebook will emerge, the
inertia at this point is too big and you would need a huge critical mass of
people (and organizations) to make it useful. Hard to attain. The only
contender on the long run to FB could be reddit, because they seem to be
moving in that direction with the new profiles and so on. They have almost
all the features that make a (general purpose) social network attractive,
the amount of users, and the content.
Regarding the question if the WMF should build a social network for the
masses, I don't think it should. A general purpose social network is mainly
used for sharing personal events, viral stories, cat pictures, and so on.
It does not offer long-term cultural value. A more interesting approach
could be a niche social network, like a *social **learning network*. It is
related to open knowledge, it offers some cultural value and it doesn't
attract the same kind of idiocy that general networks attract.
A social learning network could be oriented to life-long self-learning
where users would share stories about what are they discovering each day,
groups, creation of materials, etc. It could be said that users are already
discovering new knowledge in our sites, but they have to go to other
websites to talk about it... (for instance /r/wikipedia)
Another possible kind of network, could be one geared towards *governance
and public oversight*. This is perhaps more interesting for governments,
institutions and organizations, but still in the realm of the Wikimedia
movement, because we also need some kind of social governance to build
understanding and consensus both ways bottom-up, and top-down, and
inter-organization. Not that we don't do it already, but perhaps with
specific tools it would be easier.