From allusions to illusions, fakery to forgery, Facebook is an arena for social performative play. One would do well to ensure the secrecy of one's password and to log out with consistency, because you (yes you!) could be the next victim of identity appropriation and warping of the most embarassing variety.
This subject comes to mind in light of today's Facebook experiences: a high school friend of mine had suddenly become a black lesbian. Also, it was apparently her birthday, and in the hour or two it took for her to realize what had occurred, several friends had posted somewhat confused birthday greetings on her wall.
This is not the first time I have witnessed this particular form of public humiliation. You have been warned.
It could happen to you.