At any moment, Justin Bieber uses 3% of our infrastructure. Racks of servers are dedicated to him. – A guy who works at Twitter
The employee goes on to say that his "account receives more than 60 @-replies per second for a while after he tweets, which is something Twitter wasn’t originally designed to handle". Therefore the next time I see a Fail Whale on the site, I'm blaming Justin Bieber. Unless of course something bad has happened to his pretty little face in which case I welcome you Fail Whale into my home.
Source: Mashable