Now Playing: 09-13-13 Marketplace - Twitter's IPO and Sarah Jessica Parker's new shoes

Twitter is going public. It announced the news yesterday, in a tweet, and now the world is all a-twitter about how good an investment the company might really be. Problem is, no-one quite knows how it makes money, and the company isn't telling. At least, not yet. Oh, and Sarah Jessica Parker has a new shoe line. Better late than never.