Its difficult to get accurate data reporting on 3's traffic, but its important because 3 has 40% of the UK broadband mobile market (over a million dongle users), not the tiny smartphone browsing usage. It also now has 12,000 base stations, with a lot of HSDPA to improve the previously patchy experience.
In July, they reported 250TB of data - trivial by fixed network standards though its mainly used by laptop users - and the 6% Windows Update figure matches my own usage - the laptop decides to download about 60MB in every GB I have (which is monthly use for normal users, I have a 3GB cap).
The Guardian's reporting is 'exclusive' (12 days after WhatMobile's!), and their data suggests 1% of data was iTunes, 3% Facebook, 2% Farmville and other Zygna games. From Whatmobile, it seems about 1% is Skype and MSN - which is high as its hard to make good Skype calls on 3's network. Google and YouTube together make up less than 1%. Notably, voice calls use up only 3% of total capacity - that's what the cashcow really sucks out of backhaul - next to nothing.
Add up all those numbers, and that's 17%. Yup, 83% of mobile broadband is other stuff - and I'm guessing BBC iPlayer might be quite a lot (though its only really good for radio on 3), but also other peer-to-peer uses, and email. After all, 250TB between a million people doesn't go far, in fact that's 250MB each.
So (despite shock-horror Guardian claims that they may soon throttle and otherwise breach net neutrality) it may be a while before the network ever needed to consider traffic management - after all, they charge per MB if users exceed their cap. Sit back and enjoy the money flowing...