I have several Facebook identities. I use them sporadically when necessary, and only for specific needs. None of them are even closely related to my 'real' name.
Sure. Despite having qualms about its existence, I recognize Facebook as a somewhat useful utility, until a better option becomes widespread.
The only way for me to use that utility in way that protects my privacy and anonymity is to have several (quasi-fake) identities there, and never provide the machine with more data than I need to complete my task (read up on an event, manage a group I run, etc.)