Mark Zuckerberg and the other folks behind Facebook have had a very good Christmas this year. Traffic analyst Hitwise (via ReadWriteWeb) has announced that, for the first time ever, Facebook was the #1 most-visited website in the U.S. on both Christmas Eve and Christmas Day. Last year, Facebook lagged behind Google in the #2 place. Facebook is much more than another social networking website. It's grown to become the nexus of communication for millions of families across the country. While Google and Yahoo! Mail both receive more hits than Facebook throughout most of the year, the rules change on holidays. No site benefits more than Facebook from people's desire to talk with their loved ones during the holiday season.Much of Facebook's early success can be attributed to its highly private nature. As it has matured though, FB has opened up more and more. At this point, the idea of Facebook as a "private" network is long dead and buried, yet traffic continues to rise. If December's controversial "security update" didn't hurt the site's growth, I'm not sure what will.