We came in this morning and had a bit of a shock when we saw a big dip in our traffic graphing yesterday evening, a little searching showed that YouTube had taken a massive hit which was visible in our peering links to Google, showing over 2Gbps of traffic lost for around an hour... 
After a quick look online at a few news articles and the YouTube Twitter feed we found out we didn't break anything - cue sigh of relief! Streaming has grown to such an extent that it now takes up to 50% of our traffic at peak time. YouTube is the most popular application with BBC iPlayer coming in second which peaked at 3Gbps yesterday. With reports that IPTV is predicted to treble and the imminent launch of YouView, can we ask YouTube to break things overnight next time, instead of at peak time?! 
Tweet Edit: To clear up any confusion, the graph above only shows traffic to Google servers, not all internet traffic.
YouTube goes down!