Useful summary of the challenges (and opportunities) in social networking. He's written two other good summaries too:<p><a href="http://markmhendrickson.com/three-pillars" rel="nofollow">http://markmhendrickson.com/three-pillars</a><p><a href="http://markmhendrickson.com/content" rel="nofollow">http://markmhendrickson.com/content</a>