There are some users currently (1:50 PM GMT time) reporting that Facebook is down, via Twitter. It is not clear, however, what's happening, because there are other users reporting that Facebook works just fine for them. I have to mention that Facebook works for me quite well. Downrightnow.com, which is the website that monitors lots of services and reports if a service or another is working or not, is currently displaying Facebook as "Likely Service Disruption".
This state comes from users that reporting both on Twitter and on downrightnow that Facebook is down, while the Facebook officials didn't confirm (yet) that their service has any kind of problems.
If you want to see the progress of Facebook, just follow downrightnow.com. If you are an user of Facebook, please leave a comment telling us either if you have problems in accessing Facebook, or if works fine for you.