This article states:
The analysts determined YouTube’s bandwidth costs by assuming that 375 million unique visitors would visit the site in 2009, with 20 percent of those users consuming 400 kilobits per second of video at any given time. That works out to 30 million megabits being served up per second. That’s a heck of a lot of bandwidth to devote to videos of sneezing pandas.
Do you honestly believe that YouTube is sending out 30 petabits per second (to put it another way, fully saturating over 200,000 OC3 connections)? That on average, every single user who counts as a unique visitor in 2009 spends 20% of 24hrs = 4.8 hours actually downloading video, every day of every week?
Update: the quoted article indeed gets it wrong, though it appears the original Credit Suisse analyst report was estimating peak usage, not a running average. Still doesn’t smell right. Updating the article and title to point the finger at the right people.