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When choosing to open the removable media with an application, or open the removable media itself (to work with the files inside), you’ll be "mounting" whatever it is. Exceptions are when you’ll be writing to a CD or DVD, or (re-)formatting a USB drive. In those cases, you’ll want to chose Cancel.
Removable media should be unmounted before physically removing it from the computer. Click the "eject" symbol that appears to the right of the removable media's icon and wait a few seconds before physically removing it from the computer.
Save early, save often. Save now. Nothing is more frustrating than having several hours (or even several minutes) of work lost because you didn't save.
Systemback makes backing-up system and user configuration files easy. Make restore points to take a snapshot of your system at a particular point in time. Later you can use them to restore your “system back” to the way it was. Other GUI backup applications include Amanda, Back In Time or DejaDup.
Also see BackupYourSystem on the Ubuntu Community Help Wiki