You back up your system regularly, right? Well, you would. If you had a better way to do it. With Mac OS X Leopard and Time Machine, not only can you back up and preserve everything on your Mac — [...]

You back up your system regularly, right? Well, you would. If you had a better way to do it. With Mac OS X Leopard and Time Machine, not only can you back up and preserve everything on your Mac — including priceless digital photos, music, movies, and documents — without lifting a finger, you can go back in time to recover anything you’ve ever backed up.
Set it, then forget it

The first time you attach an external drive to a Mac running Mac OS X Leopard, Time Machine asks if you’d like to back up to that drive. Set up the drive and Time Machine takes care of everything else, automatically, in the background, so you can get on with your digital life.

http://www.apple.com/macosx/leopard/timemachine.html