Now that Apple has released OS X 10.9 Mavericks, you might want to consider creating a USB install drive for clean installs and future use.
If you're an Android whiz, here's your chance to earn some serious coin. But you'll have to code fast if you want the full $5,000.
New PowerBook G4s ship with Bootable DVD-ROM
Bootable expansion bay CD-RW drives
Retrospect issues: Duplicate backup not bootable?; more
Check your chipset.
Several users have reported an issue in which users experimentation with or inavertent modification of permissions on key system resources renders the system unable to boot.
BootCD creates custom bootable CD with a Finder!; Related bootable CD and copy volume follow-ups
NVidia 6800 and Mac OS X booting problems: creating a bootable CD
Apple shipping 2003 Mac non-bootable CDs with AppleCare package