[joebadmo]

Well, if we don't work together, we wouldn't share a work friends group.

It's true that a places metaphor is a bit less granular, but I think it makes it easier to understand how things are being shared than a bunch of one to many connections that overlap to varying degrees.

Also, there's no reason you couldn't have both, since the places metaphor is really in practice just a subset of everyone having individual group lists.