Never put your data into anything you don't know how to permanently delete it from.
Today's illustration is Facebook, whose TOS used to indicate when you closed your account, any rights they claimed to your content expired. Not so anymore, the following language has been removed:
You may remove your User Content from the Site at any time. If you choose to remove your User Content, the license granted above will automatically expire, however you acknowledge that the Company may retain archived copies of your User Content.( Facebook's New Terms Of Service: "We Can Do Anything We Want With Your Content. Forever." )
† Contrast with my First Rule of the Internet: Don't fuck with the Internet. E.g. see http://www.kenny-glenn.com/.