There is an interesting option on the latest version, 9.04 (Jaunty), in
the System/Administration menu, if I remember, on the Live CD to create
a bootable USB version of Ubuntu. Works fine. I carry one when I'm
traveling, in case I want to use Ubuntu on someone else's Windoze
machine. If it can boot from a USB device, it will boot Ubuntu and give
you a functional system, like the CD, but with any excess capacity on
the USB drive as storage, which is an improvement on a Live CD for a
functional system.