Some users should be currently getting an error when logging onto Facebook that says that this account is not accessible due to a site error. The extent of this problem is unknown as of now, and it is not known by when this will be fixed.
As of now, clicking the Account button at the top-right tells you the account name and displays your profile picture, but none of the links seem to work. Chat shows the friends online, but it is uncertain whether the people on the other end receive the message.
We should expect an update from Facebook very soon.