Due to an issue with Facebook Connect, for a brief period visitors to sites like CNN and Yelp were landing on a Facebook error page instead. This issue only affected people signed into Facebook when they visited the sites. Which more or less means pretty much everyone. Sure you could fix the issue by signing out, but who has time for that.
In the past the only way social media was able to take other sites offline was with traffic. There is even a word for this, the Slashdot effect. Facebook certainly seems to have come up with a real game changer as far as this is concerned.