If you are running OSX 10.5 and have Time Machine configured to backup your system and you see that you are missing an email that you may have accidently deleted, you can recover it very easily.
With Mail.app running and the front-most program, enter Time Machine and you'll see the starry background interface but instead of Finder folders to sort through, you are in Mail. You can scroll back to the date you remember having the email and then restore it. It will restore into a folder in the On My Mac category so you can re-file it where you want.
The same thing also happens when you are in Address Book and iPhoto. Time Machine lets you scroll through the Address Book and iPhoto interfaces finding the information you're missing.
Unfortunately this cool tie-in with Time Machine doesn't exist with all apps, but it can be really handy dealing with lost information instead of lost files.
If you want to change the backup interval from 1 hour to something that is better suited for your environment and needs, there is a great program called TimeMachineEditor that can be used to change it. For example, one of our clients' servers has a LOT of file activity on it and doing hourly backups can put a little extra load on the server than we'd like so I used TimeMachineEditor to change the interval to every 3 hours. Files still get backed up at an interval that is acceptable for them and there isn't a frequent performance hit.
Another example: If you are using a TimeCapsule or an OSX Server as the target of your TimeMachine backups, you may not want to tie up the network with a lot of traffic frequently during the day. TimeMachineEditor can change the interval for your computer so that it is backed up at a certain time of day. I have one office with 5 computers set to backup to their shared TimeCapsule at staggered times after business hours. 5:30, 6:15, 7:00, 7:45, and 8:30. All the computers get backed up and the 45 minute window I give each one is plenty of time to backup that day's changes. It's a handy tool to have.
WARNING: TECHNICAL DETAILS AHEAD...
Did you know that TimeMachine doesn't backup EVERY file on your system? There are some files that don't need to be backed up (like Cache files). And there are files that can't be backed up because they are constantly in use. Then there are files that aren't practical to backup in the manner TimeMachine does - VMWare Fusion automatically excludes the Virtual Machine hard drives from TimeMachine because even though your virtual machine sees thousands of files on its virtual hard drive, the MacOS only sees a single monolithic file that changes every time it is opened - even if you don't actually DO anything within your virtual machine. You'd have hundreds of backups of files that are many gigabytes in size for no good reason.
This MacOSXHints.com article gives some insight into how things are excluded.
This article goes into deeper detail about the system-level files and folders that aren't backed up by TimeMachine either.
If you are running OSX Server and are backing it up via TimeMachine, you need to be aware of these things because the Mail database isn't backed up unless you use a program called mailbfr (currently not compatible with 10.6). MySQL databases should be backed up using backup tools specifically for databases. See mysql.com for more info.