Facebook turns five and Al Mohler has thoughts about it and social networking in general. By the way, Dr. Mohler is one of my facebook friends. 
Dr. Mohler has 8 suggestions for “safeguarding the social networking experience.”
1. Never allow social networking to replace or rival personal contact and communication. God made us to be social creatures that crave community. We cannot permit ourselves to substitute social networking for the harder work of building and maintaining personal relationships that are face to face.
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3. Never write or post anything on a social networking site that you would not want the world to see, or anything that would compromise your Christian witness. There are plenty of young people (perhaps older persons now, too) who are ruining future job prospects and opportunities by social networking misbehavior. The cost to Christian witness is often far greater.4. Never allow children and teenagers to have independent social networking access (or Internet access, for that matter). Parents should monitor, manage, supervise, and control the Internet access of their children and teens. Watch what your child posts and what their friends post.
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8. Do all things to the glory of God, and do not allow social networking to become an idol or a display of narcissism.
Go read the other four at the link above.