When you update information, we usually keep a backup copy of the prior version for a reasonable period of time to enable reversion to the prior version of that information. …
… Even after removal, copies of User Content may remain viewable in cached and archived pages or if other Users have copied or stored your User
Access and control over most personal information on Facebook is readily available through the profile editing tools. Facebook users may modify or delete any of their profile information at any time by logging into their account. Information will be updated immediately. Individuals who wish to deactivate their Facebook account may do so on the My Account page. Removed information may persist in backup copies for a reasonable period of time but will not be generally available to members of Facebook.
Here is the clearer and more comprehensive version from the new proposed policy:
Viewing and editing your profile. You may change or delete your profile information at any time by going to your profile page and clicking “Edit My Profile.” Information will be updated immediately. While you cannot delete your date of birth, you can use the setting on the info tab of your profile information page to hide all or part of it from other users. …
Deactivating or deleting your account. If you want to stop using your account you may deactivate it or delete it. When you deactivate an account, no user will be able to see it, but it will not be deleted. We save your profile information (friends, photos, interests, etc.) in case you later decide to reactivate your account. Many users deactivate their accounts for temporary reasons and in doing so are asking us to maintain their information until they return to Facebook. You will still have the ability to reactivate your account and restore your profile in its entirety. When you delete an account, it is permanently deleted. You should only delete your account if you are certain you never want to reactivate it. You may deactivate your account on your account settings page or delete your account on this help page.
Limitations on removal. Even after you remove information from your profile or delete your account, copies of that information may remain viewable elsewhere to the extent it has been shared with others, it was otherwise distributed pursuant to your privacy settings, or it was copied or stored by other users. However, your name will no longer be associated with that information on Facebook. (For example, if you post something to another user’s profile, and then you delete your account, that post may remain, but be attributed to an “Anonymous Facebook User.”) Additionally, we may retain certain information to prevent identity theft and other misconduct even if deletion has been requested.
Backup copies. Removed and deleted information may persist in backup copies for up to 90 days, but will not be available to others.
Read more on Facebook.