I don't use Twitter or Facebook, and I don't know how they work. All I know is that people use them to waste time letting the world know "I'm going to the grocery store" or "I'm watching reruns of Hogan's Heroes". I hear frequently that they mine their users' personal info to a deep degree. Yet frequently I read about Twitter and Facebook being critical communication tools during emergencies that have cell service.

How does this work? If the infrastructure is intact, what do Twitter and Facebook do for you that a cellular call, text, or email don't do? If these tools are useful, how do you use them without giving up your personal info to the cloud?