Mark Zuckerberg's social-networking juggernaut is the smallest and youngest of the Fab Four, but that's just what makes it threatening. For starters, it's that rare Shangri-la of Silicon Valley opportunity—a pre-IPO sure thing that will guarantee everyone who enters its doors a stock-market fortune. It's no surprise, then, that Facebook has been steadily siphoning engineering talent away from Google and every other giant in tech. Even more alarming for its rivals, Facebook is already showing monster results in the ad business; revenue for the first half of 2011 reportedly stood at $1.6 billion, doubling the previous year's figures. Beyond the numbers, talk to ad people and they'll tell you that Facebook is now the epicenter of their digital campaigns, from display ads to brand pages.
That's the prelude. The promise of Facebook lies in its servers, in the data it collects about how we interact with one another and with brands. Call it the "social graph," call it the "taste graph" (by aggregating our "Likes," Zuckerberg knows our desires), call it the "activity graph" (by analyzing our check-ins and our statuses, Zuckerberg knows what we're doing). Whatever you call it, don't forget to call it unbeatable.
800,000,000 Facebook now boasts more than 800 million users around the world. More than half of them log in every single day, and more than 2 billion posts a day are liked and commented upon.