Another key to a successful hackathon is showing employees that the executive staff supports it, Keyani says. "If you're going to throw a Hackathon, it's really important that people from all over the company are involved," he says. "Get members of your executive team to show up, at least for part of the time."

Make it fun, too. Hackathons at Facebook always kick off at 7 p.m. on Tuesdays and wrap up at 7 a.m. the next morning. The company orders food from its favorite restaurants and a few kegs. In the morning, teams that are still hacking will go out to breakfast together before heading home for a few hours of sleep.

Two weeks after the hackathon, participants reconvene for the "prototype forum"--a meeting in which each group presents their project to Mark Zuckerberg and other executives. Keyani says the two-week timeframe gives groups the opportunity to fine-tune their hack before presenting it.

"You have three minutes to get the demo working, say what it is and why you've developed it," Keyani says. "Because we have so many people, we're strict with the three-minute rule. We'll pull the plug on you if we have to, even if you're Mark Zuckerberg."