According to Hitwise, an internet traffic monitoring group:

“Facebook was the top-visited Website for the first time and accounted for 8.93 percent of all U.S. visits between January and November 2010. Google.com ranked second with 7.19 percent of visits, followed by Yahoo! Mail (3.52 percent), Yahoo! (3.30 percent) and YouTube (2.65 percent).”

The rise of Facebook to the top seems inevitable since more people rely on websites with shared information with other people than what we would find in algorithm-driven search websites.  This could also mean that people trust online content (videos, photos, etc.) that is shared by people within their network more than going to a random website via a search.

Think of this as an example. People will watch YouTube video embedded in a friend's Facebook wall. Since they are on Facebook, they will decide to post their thoughts about the video underneath that video, share to other friends, etc. These activities will count towards Facebook’s traffic as the said video is determined as trusted content from a friend.

Facebook applications, especially online games, are another factor that heavily contribute to its popularity.

For this year, we are expecting a tighter competition between Google and Facebook. With Facebook setting the trend, don’t be surprised if Google keeps trying to place a dent into the social web market. Its previous attempt with Google Buzz was timid at best.