There are several challenges that need to be solved when building social applications. The ability for users to invite friends and share data amongst themselves is one example. If you want to add support for loosely-connected portable devices, synchronization and conflict resolution add significant complexity on top of an already difficult problem.
The Live Framework is a set of libraries and services for building connected applications that can reach millions of users. Live Mesh is a set of services for synchronizing user and application data between multiple devices and multiple people. I’ve recently posted a short screencast that illustrates using these technologies to make building ‘Always-Available Social Applications’ much easier. You can view the 10 minute screencast on Channel 9.