According to Wikipedia’s Facebook page their website was down today for an undisclosed amount of time. They attribute the outage to overheating problems in their European data center which caused many of their servers to shut themselves down.
They state that they also experienced problems with their fail over plans and DNS resolution issues. Those issues were quickly resolved but they did expect some extra down time before access was completely restored.
As of 1422 PST they appear to be up and running.
John "Mike" Wright