Anil Dash predicts the outcome of the days following the forthcoming rush on Facebook usernames:

June 13, 12:45am: TechCrunch discovers that one of its writers can’t get his preferred spelling for his name, and notices that registrations in the system are running a bit slow. A Twitter search reveals four other people discussing the same problems, and one person that can’t get to the feature at all. The phrase “The Facebook Username debacle” is first used, and becomes the preferred sobriquet for the feature forevermore. 70% of commenters mention that “Facebook Username” can be abbreviated “FU”, and each thinks he is the first to think of it.

Almost certain to happen.