7. Test your backups and verify space periodically
One of the most noteworthy new features in Leopard was Time Machine , which makes maintaining backups as easy as connecting an external hard drive or Apple's Time Capsule and performing a couple of clicks. Although Time Machine is generally problem-free, it's a good idea to periodically (once a month is a good rule of thumb) test your Time Machine backups (or any backups). This allows you to be sure that your Mac is backing up properly before an emergency occurs.
On the backup front, there are a couple of other things to keep in mind with Time Machine. First, consider periodically verifying the directory structures and SMART status of the hard drive storing your backups (and repair as needed) for much the same reason as testing the backups themselves -- to make sure they will be available if you ever need them.
Most people probably don't need to do this on a terribly frequent basis, but it can be a good habit to do along with checking your primary hard drive or verifying the backups themselves.
Second, keep tabs on how much space is left on your backup drive. Because Time Machine keeps multiple generations of backups, it is possible to fill a rather large hard drive pretty quickly, especially if you work with a lot of large media files. Time Machine is designed to intelligently prune backups to provide you with a mix of older snapshots and more recent snapshots of your data when the drive grows full. The intent is to preserve the widest time frame possible.
If the drive becomes completely full, intelligently or not, Time Machine removes past generations of backups to make room for new ones (and alerts you to the fact). Keeping tabs on the drive's free space will give you time to deal with the situation -- typically by buying a new Time Machine drive.
Note: One way to conserve space on a Time Machine drive is to exclude Leopard's system files or folders containing large files that change frequently, such as the scratch folders used by many professional media and graphics applications. You can make this adjustment in the Time Machine pane in System Preferences.