Compete shows that Facebook gets 104 billion page views a month, 2.29 billion visits from 125 million unique users. Those users spend a total of 10,230,335 hours per month (September 2009) surfing the site.
Doing the math: 10,230,335 hours per month divided by 30 gives the total number of hours spent per day on Facebook = 341,011.2 hours = 39 years/day!
Does this mean that, roughly, Facebook users all together spend 39 years per day on Facebook.com? What a waste!