Gigabytes Per Month per Person

"Reliable data about internet traffic is hard to come by. One of the better sources is Cisco's annual Visual Networking Index, which was published on June 1st. Internet traffic, the world's biggest maker of networking gear predicts, will quadruple and reach 80.5 exabytes per month (80 exabytes would fill 20 billion DVDs) by 2015."

Chart from The Economist blog Daily Charts

original article link and titles 

Consumer internet traffic: Data guzzlers -  How the world will use the internet in 2015