Comment 24 for bug 782389

A couple of notes here :
You *can* boot a live session using both a USB and a CD, here are the steps :

Note 1 :
Step 1 : Burn ISO image to a CD
Step 2 : dd or use usb-creator to write ISO to a usb thumbdrive
Step 3 : Insert both the CD and the USB disk during the boot sequence and hold down 'C' to boot the CD
Step 4 : Wait for everything to load and proceed with installation ( At this point, you can remove the CD since the session is being run from the USB thumb drive )

Note 2 :
Interestingly, my DVD/CD drive does work if you hold the 'option' key during the boot sequence, if you use reFit the drive is not recognized. I would highly recommend using the option key to boot the other OS because that way most of your hardware works out of the box ( I couldn't get my backlight controls to work either with reFit )