Facebook has a real name policy that does not allow pseudonyms, and they technically can revoke your account for using a fake name. However, that is soon going to change. Prominent users will be notified to verify their account, and when they do, they will be given the option to display a pseudonym, instead of their birth name. This is great for celebrities who are more known by their nickname, not their birth name (Lady Gaga, Prince and Madonna, for example).
When a person applies for a verified account with an alternate name, Facebook will manually approve them to make sure that everything is legitimate. This prevents people from pretending to be the celebrity, and makes it easier for fans to find the person they are looking for. Verified accounts will require a valid, government issued photo I.D.
The one problem with this change is that everyone is still required to give their real name to get a verified account. This might be a problem for some, who use their pseudonym only. They may not want to advertise their real name, and forcing them to do so may deter them from using this option.
Facebook is obviously trying to compete with Twitter with this move. Twitter allows celebrities to verify their account using any name they choose, and Facebook seems like they would like a piece of that action.