Yeah, the DVD-R method works, but has its limits if you have a larger chunk of data in your users directory, and don't want to loose your home folders.
Personally, I like the firewire/CCC method, too. I always make a clone before major system changes, and whenever I feel like it to protect the minor data changes going on in my home folder.
Not only are you able to completely roll back to the last known good setup, but you can be started up and running from your backup in less than a minute, with no perceptable difference from using the internal drive.
Peace of mind. It's all about peace of mind.