Oh yeah, if the GM knows all the people in my character's backstory it just becomes more people for them to use to torture my character (I've had more mentors/siblings/parents/friends killed off or turned evil than I care to think about just now). I don't always have all the backstory worked out before a game starts for multiple reasons, but by the end, between my own filling in the blanks and the GM messing with me (ask me to tell you my Star Wars character's backstory I dare you) it gets mighty complex. And by the end my character are so angst filled and often insane, I find them like crack to want to write about. I'm an angst ho, I admit it, luckily my GM's tend to love that about me, and my characters would hate us both for it if they got a say.