Facebook population: 10 million+
September 2006 was a huge month for the fledgling social network. Facebook was opened to the masses; you no longer had to be enrolled in high school or college to sign up. And it introduced a "news feed" that allowed members to see what all their friends were up to -- resulting in a privacy backlash from Facebook faithful. That in turn prompted the first public mea culpa from Mark Zuckerberg: "We really messed this one up." It wouldn't be the last.
The Good: Now everyone and their grandmother can have Facebook account
The Bad: Grandma just sent you a friend request