At 12, Seth Priebatsch started the deal-finding site Giftopedia; he claims it "failed gloriously," although it turned a small profit. At 17, he launched the print-based marketing site PostcardTech. "A good idea, but not a big idea," he says. Scvngr, however, is a big idea—big enough to attract north of 1 million users in less than nine months. Scvngr turns check-ins into interactive contests with challenges and prizes. Now 22, Priebatsch is already onto the next big idea, a loyalty program called LevelUp. It's another step in the "chief ninja's" plan to "add a game layer on top of the world."