YouTube. Http/1.1 Service Unavailable.

The world’s most popular video destination is off to a shaky start today — many users are being greeted by a “Http/1.1 Service Unavailable” message upon arriving at the homepage.
We’ve also noticed that many videos embedded on third-party sites like Mashable appear to be failing to load, though both problems seem to resolve themselves after a number of browser refreshes.
Meanwhile, plenty of people are discussing the YouTube problems on Twitter.