facebook guide lines on user names

Usernames were created to make it easier for Facebook users to identify their profile and share with others. Facebook encourages users to consider the following when creating a username:
Your username should be as close as possible to your true name (e.g., Jsmith or John.Smith). Names such as CoachJohn, BlondeJane, etc. don’t clearly identify you as well as your true name.
Usernames can only contain alphanumeric characters (A-Z, 0-9) or a period (".").
Choose a username you will be happy with for the long term. Usernames are not transferable.
Your username must adhere to Facebook’s Statement of Rights and Responsibilities.