Well, we knew this was going to happen. With a high user engagement and a massive userbase build up, Facebook has just slipped pass through Yahoo to become the no.2 most popular website in the U.S. Latest data from Compete.com shows that Facebook is not only raking up userbase but user engagement as well as it had  133 million unique visitors last month. Yahoo's unique visitors were pegged at 132 million, while Google still sit on top.