Today, Facebook boasts some 250 million registered users and is , depending on who's counting. Three years and two CEOs later, Yahoo is still struggling to survive.

People think Steve Jobs invented the iPod. He didn't, of course. Jobs merely said yes to engineer Tony Fadell after the folks at for a new kind of music player in the fall of 2000. (Fadell's former employer Philips also turned him down.)

By then MP3 players had been around for years, but was slightly different: smaller, sleeker, and focused on a content-delivery system that would give music lovers an easy way to fill up their "pods." (Jobs is famous for driving the design of the iPod.)

Today that content-delivery system is known as iTunes, and Apple controls some 80 percent of the digital music market. Fadell worked at, and eventually ran, Apple's iPod division until November 2008. Real Networks is still a player in the streaming-media world, but its revenues are a fraction of what Apple makes from iTunes alone. (Photo: Courtesy of Apple)