People like to hype up the threat that Facebook poses. Is it an invasion of privacy? Only if you hand over a silver platter of all your personal information, which most people do. Do they retain your user data indefinitely? They seem to, though there's a community on FB that's supposedly dedicated to spreading the word of how to permanently delete your account and all attached or stored information.
It doesn't work, of course. On Thursday, August 12, I set my own account to delete. I was just tired of it--people use it as a crutch to disseminate personal updates with none of the personal attention of directing it to a specific person. You just upload photos of what you did that weekend, then act all offended when your 400 friends didn't logon to seek you out and appraise themselves of your doings.
My feelings are, if you want someone to know, then you engage them in conversation and tell them about it, but apparently this is quite unreasonable: any time I talk about the dozens of concerns other people have written about Facebook, I've been accosted by small groups of friends who deride my opinions and argue that I should just stay where I am and quit worrying about things.
Wow, if there's any one statement that induces my paranoia, it's something along that line. So I gave all my friends and family ample notice and means by which to stay in touch with me--largely ignored--and terminated my FB account. FB says that your account will be purged if you do not login for 14 days, so I set up a calendar reminder to check it out 16 days later.
Facebook has no interest in deleting anyone's account. It's a free service so they have no contractual obligation to its users (you wouldn't know that from the astronomical sense of entitlement its users express on a regular basis, as pertains to online games or periodic rumors of FB becoming a paid service). Anything they promise to do, or flippantly suggest they might do, is a favor at best. In practice, it's just noise.