Airdate: 01/13/08  At 23, most people are worried about what to do on Saturday night. Facebook founder Mark Zuckerberg has other worries, such as whether to take his company public or how to develop profitable advertising. Lesley Stahl talks to the Harvard dropout, who may be the only billionaire who sleeps on a mattress on the floor of his one-bedroom apartment.This product is manufactured on demand using DVD-R recordable media. Amazon.com's standard return policy will apply.