The social network crashed this evening in spectacular fashion and is still down more than 15 minutes after the intial crash, as people take to other social networks like Twitter (ironically) to vent their frustration and spread the news - http://twitter.com/search?q=%23facebook
Facebook have not yet released any information on their own Twitter feed and there are thus far very few articles covering the story: http://twitter.com/facebook
Facebook later released a statement about the outage and apologised for the interruption:
Earlier today we made a change to our DNS infrastructure and that change resulted in some people being temporarily unable to reach the site. We detected and resolved the issue quickly, and we are now back to 100 percent. We apologize for any inconvenience.