User friendly and deletes your data

Apparently there are circumstances where Apple's Time Machine backup product will delete all of your old backups to make room for some new data, like after an upgrade or when attaching a new drive to the system.

This is exactly why I use tapes. See the following dialog:

OS X - "Please insert week 3 user data backup tape, I need to wipe it so that I can replace your backups with copies of OS X binaries though you already have those on DVD"

Me - "No"