It's not clear why Yu is leaving now. He raised nearly $500 million for the company, and was looking for more. But a few things are known: Zuckerberg has repeatedly said that the company's focus is on growth rather than making money. He has made a habit of quickly cycling through executives. Former Facebook COO Owen Van Natta, who left after an apparent demotion, is a notable example.
The question is who's next? Jonathan Heiliger, a dotcom-era Internet wunderkind now in charge of Facebook's vast technical infrastructure, has long been said to be restive. COO Sheryl Sandberg, the Google veteran splashily hired last year, might be called to account if Facebook's sales don't catch up with its user growth. As the door to Facebook's executive suite keeps swinging, it seems like only a matter of time before people start asking questions about the prickly, isolated 24-year-old at the top.