Summary: SAN FRANCISCO (AP) , Facebook CEO Mark Zuckerberg reaped a gain of nearly $2.3 billion last year when he exercised 60 million stock options just before the online social networking leader's initial public offering. The windfall detailed in regulatory documents filed Friday saddled Zuckerberg, 28, with a massive tax bill. He raised the money to pay it by selling 30.2 million Facebook Inc.
