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Back in 2007, Apple put a YouTube client on the iPhone and created a memorable site; now comes word from Google that 40% of the traffic coming to YouTube to view streaming videos, is viewing the video from a mobile device. That is up from last year's 25% that viewed You Tube videos on a mobile device. In 2011, that figure was only 6%.
Source: http://www.phonearena.com/news/40-of-You-Tube-views-now-come-from-a-mobile-device_id48405