If you go through the process of trying to delete your account they do all this crazy stuff to try to dissuade you. One example - they show you pictures of your friends with comments like, "friend x will really miss you." The process tries to get you to just disable it. If you go through with totally deleting it you have 14 days to change your mind and then it is supposed to be permanent. Ars had an article a few months back showing how your data (specifically pictures) could still be found even after deleting your account, FB claimed they solved that issue, but I'm not sure.
Hopefully this is helpful.