Mark Zuckerberg sure is popular. Facebook, the online social networking site, has reached 500 million members, making its Web population equal to the size of the world's third largest country. Birthed in a Harvard dorm room in 2004, the site's number of users has accelerated in the past year. In January 2009, Facebook had 150 million members. The company isn't suffering for ambition: last month, Zuckerberg, the founder and CEO, said that the site would hit one billion users. This fall, Aaron Sorkin will release a movie depicting the rise of the company. The tagline? "You don't get to 500 million friends without making a few enemies."