In Zuckerberg's post he says that more than 150 million people around the world are now actively using Facebook, including "people in every continent—even Antarctica." He goes on to say that "If Facebook were a country, it would be the eighth most populated in the world, just ahead of Japan, Russia and Nigeria."
Facebook, however, is not a country (see, I'm very insightful). And, no offense to my dear friend Zack, but I don't know that either of us are artfully skilled enough to configure a country design and plop it on the globe in a believable manner. However, what Zack did was take Facebook's existing user numbers and plop them into an already existing map:
What the above represents, according to Zack's research, is that the entire population of France, Switzerland, Austria, Italy and Belgium roughly make up every Facebook user in the world.
For all of it's power, however, Facebook isn't really a global network, compared to say, Hi5. Facebook experienced tremendous growth in 2008 and is expanding beyond it's safe and comfortable network of U.S. users. I expect in 2009 Facebook will have to put it's money where it's statistics are and try to engage more overseas users if it is truly shooting for world socnet domination.