I was thinking along the same lines, actually, in terms of a "distributed Facebook"'s similarity to Lotus Notes. However, one of the big niceties of SaaS services is that you don't bear the cost of storing and transforming all the photos, videos, etc that you upload. Replication of this data would also get quite expensive as you gained followers. And then there's the problem of bandwidth in the US. Seems to me there are some infrastructural problems with a distributed Facebook model that require some more thinking than just "lets run a server on people's home machines" (e.g. Diaspora)