'Perfect' Mac OS X backup procedure
Backing up my user files under Linux is easy, if everything in /home/mark fits on a DVD-R. A Linux re-install is quick and then overwrite /home/mark. I usually install applications that I build from source in my ~/bin directory and Ubuntu's package manager makes it quick enough to restore other required apps (PostgreSQL, etc.)
The Mac is not so simple because installed applications store frameworks in the system library, etc. Still, it it easy to make a reliable backup, assuming that you have an external FireWire (or I suppose an USB) disk drive:
Make sure that there is room on your external disk for your home directory and another 5 gigs
Plug in your external backup disk, and restart with your install DVD
Install OS X, choosing the external drive
When the installer asks if you want to import previous user data, say yes and select your internal disk that contains your system and user account
Reboot using your external disk and run software update
Pack away your external disk as a backup of your working environment - preferably off site for extra protection.
If you run this procedure while you are reading or watching TV, this is a low overhead operation - cumulatively just takes about 10 minutes of time (about 1 hour wall clock time). An external disk can obviously also contain other backups of large video files, etc. in addition to your OS X and user setups.
Nothing is for sure in life, but external disks are likely to have longer shelf life for your digital assets than CDR-R and DVD-R media, but using both, and off site backup on remote servers, etc. is also a good idea.
Because of the (hopefully) very high reliability of external FireWire (or USB) disk drives, I also copy important Windows and Linux backup files to an external disk using either my LAN or DVD-R backups. Replicating really important files to multiple computers on your network using rsync is also a good idea.