Nielsen has released The social media report of the third quarter of 2011. This study looks primarily at social media and its users in the U.S., but also includes other relevant markets and is a good indicator of trends.
Facebook is still leading social networks in the U.S. with over 140,000 unique visitors. Already from far away, followed by Blogger, and Twitter about 50,000, with more than 23,000 minutes.
Facebook is not only the most visited but where Americans spend more time with 0.5 billion cumulative minutes when Blogger accumulated 724 million minutes. Google only collects 12.5 million minutes.
Social networks as they have monopolized the use of the network. However, it is also true that one can detect a significant bias since many users leave these applications open almost continuously while navigating.