I have a manual solution which, to me, beats Apple's Backup hands down: I created a normal folder and put aliases to my essential files in that folder. To back them up just drag the aliases onto a burnable disc. You don't even have to go and find the original files, the burnable disc will find it for you. Want to schedule the backup for every 10 days? Use iCal to remind yourself.
You still have to guess whether or not all of the files will fit onto the burnable disc, but overall the process of selecting or removing files is much quicker, much less annoying, and has most of the functionality found in Apple's Backup. Restoring is just a matter of knowing where your files belong. Not a problem for most folks. This is also great for squeezing more files onto one CD, since it would seem that Apple's Backup over-reports the size of the files being added to the burnable disc (or is it under-reporting the size of the burnable disc?). The only advantage I see with Apple's Backup is that you can seamlessly split a single file (videos) across multiple CDs or DVDs.
Be sure to review this hint if you try this. I had some unexpected things happen with aliases and copying. Nothing damaging, just unexpected.

