I've been really impressed with Ning social networks since I started using one for Sloan-C SL-NET. The primary advantages over Blackboard or Moodle are its public visibility, the ability of members to start forums and form groups, and the accessibility of RSS feeds. I'm using a Ning site for a hybrid technical writing class I'm teaching this fall. (It's private for the obvious reasons.) I've also joined a social network for educators who are using Ning in education.
