Highlighted by the latest Ubuntu Weekly Newsletter (#88), there’s a great tutorial in the Ubuntu forums for transforming an Ubuntu install into a custom LiveCD/DVD.
This HOWTO is about making a live CD/DVD from the main system on your hard drive. This might be desired if you have customized your system and want to have it on CD. It can be useful also if you want to create a recovery CD from scratch, as you can make a minimal system using debootstrap and transform it into a live CD.