Friends? Social Groups? Is this stuff documented?
 

Where can I find documentation about Friends, Social Groups, Visitor Messaging, Visitor Tracking, and some of the other new features that have been added to recent releases? (I upgraded from 3.0.17 which didn't have any of this stuff.) I can't find it in the standard documentation. Is there anything that describes what it is and how it works?

I don't want to enable these things until I know what they are, how they work, and what the implications are for performance.