Just-in-time provisioning of Drupal user accounts based on SAML attributes (configurable). Automatic role assignment based on SAML attributes (configurable). Dual mode - support for traditional Drupal accounts and SAML-authenticated accounts at the same time (configurable).
After watching Chris Messina's existential DiSo Interview, I decided to go check out a bit more about the distributed social networking stuff Chris and Steve Ivy have been working on - there are 160+ people on the mailing list now, and hundreds of threads.
Here's a little bit about the DiSo Project: