Facebook's Terms say: "You will not provide any false personal information on Facebook..."
But Facebook's registration is VERY unclear. They ask for an entry for "First Name" (not specifying whose), an entry for "Last Name" (again, not specifying whose), an entry for "Your Email" (specifying an article "Your", so presumably if they wanted my first name or last name, they would have specified "YOUR name") and an entry for "I am [Select Sex:]" (presumably asking me to predict the web developer's gender (?). If they wanted the registrant's gender, they should have said "YOU ARE [Select Sex:]", or at least make sure that the email question and the gender question were consistent. The Terms refer to the user as "You" and not "I".
Given that they have first person, second person, and no person specified on their registration page, any lawyer worth his $250/hour should be able to argue your way out of criminal charges (or even breach of contract) in using a fake name on Facebook.
A reasonable argument would be that the first time I went to Facebook, I wanted to search for a friend, so I put in HIS first name and last name, created an account, and now I am stuck with it.
Unfortunately, Facebook's very own terms restrict me from correcting this error (due to their lack of clarity and inconsistencies on the home page), as the terms say "You will not create more than one personal profile."