Looks like Facebook servers aren’t able to handle the load of their 500 million users and have been out for a while now. If you head over to this Twitter search for "Facebook Down", you will see tons of users complaining about Facebook being down.
I can confirm that Facebook is down for me too and is displaying an error saying that "An error occurred while processing your request".
This definitely looks like a big outage for Facebook, more updates to follow soon.
Update: Facebook just tweeted that the issue should be fixed for everyone, no updates on what caused it though.
We’ve resolved the tech issues that caused the site to be unavailable for some people. Everyone should now have access.
Update 2: Facebook has released a response on why the problem occurred, it turns out that it was more of a programming error which caused flooding of the DB. Read more about the details on the outage here.