Five hundred million people "are now using Facebook on a monthly basis," PC World reports, which means "Facebook has a slightly smaller population than the continent of North America," and that's "enough users to put 75 people on every one of the over 6.6 million square miles of Russia, the largest country in the world by landmass." Just a couple of PC World's "Fun Facts," and this is just one of … [Read more...] about Facebook passes half-a-billion mark