I was hoping this was going to be something where the files themselves were distributed so that they didn't take up space on everyone's machines, a la MogileFS[1], but alas.
This is always a point of pain for us: in our studios we work from a central file server, so our shiny iMacs with their 1TB drives all have about 90% capacity on them — but we don't have any easy way to pool all that extra capacity and use it even as overflow for our central fileserver.
The search continues...