Related-ish-ly, I've had a notion bouncing around in my head that it should be possible to build a fairly complete social networking interface on top of email and ical (or similar), and some kind of contact-management standard, such that the whole thing (or at least enough of it) could be rebuilt from e.g. your (possibly dedicated to this purpose?) email account when necessary, possibly in stages—say, a new installation of the application builds what it can from the last 30 days in a few seconds, then displays a populated interface while it continues digging to some arbitrary point in the past (until it exhausts caching resources it has been allotted on a given platform, basically).

An initial search has revealed a couple abandoned partially-complete efforts, but that's it.