According to Nielsen, the average Facebook user spends 7 hours per month on the social networking site. At least that was the case in January 2010. By Nielsen’s measure, Facebook blows away all other marquee web properties in terms of hours spent per month. The next closest web property was Yahoo, with a distant 2 hours and 8 minutes in January 2010.
Internet king Google had the largest unique audience in Jan 2010 at over 152 million, but trailed Facebook and Yahoo in average hours spent per user at 2 hours and 1 minute. To my surprise YouTube users only averaged 1 hour and 2 minutes per month.