It's worth nothing that Facebook's metric for user counts is active users, someone who has logged into the Facebook site within the past 30 days. This makes the metric that much more impressive, as the 500 million user count can be seen as people who are actively using the site, discounting those who have registered and never returned.
Facebook's growth continues at a prodigious rate. The site passed 250 million users nearly a year ago to date, announcing that milestone on July 15, 2009. As part of the 500 million mark, Facebook is soliciting stories from its users about how the site has made a difference in their lives.
Recently, a Hollywood movie was actually announced that will be based on Facebook! Click here to check the trailer.