I don't think it's a good idea for a person's identity to be anchored in one particular community, because people join and leave communities over time. In a generic system like Facebook, I can cut all ties with high school if I want to.
I'll write something up for Appleseed's wiki when I get a chance, for the most part they're original concepts that are being worked out within Appleseed. But basically, they work similarly to what their names imply.
Linking, Cloning: I have two accounts, on a.com, and b.org. When the two are linked, actions taken on a.com are duplicated on b.org as my b.org identity. Friends on b.org are not made aware of the existence of my a.com identity. There are subtle differences between linking and cloning that are still being worked out.
Profile forwarding: Works just like email forwarding. I leave one site, and move to another, and at the original site, I leave a forwarding address.
