An ubuntu live usb disk has problems booting in older systems, since their BIOS isn't set up to boot from USB. You have to edit the BIOS settings manually, and allow booting from your flash drive. But, this can be a problem in public places, because when they see you tweaking with their computer's BIOS, you're probably gonna get kicked out. This is a problem with mostly all live CD operating systems. The only practical way to run a linux distro off a USB disk is probably to use a Virtual Machine, unless you're running a newer computer. So, could someone develop a portable virtual machine with ubuntu built into it? And, yes I have heard of Portable Ubuntu for Windows and Portable Ubuntu Remix, but those just run the ubuntu title bar at the top of the screen, and run a few ubuntu programs. I'm looking for a full ubuntu desktop with the latest LTS release or the release of your choice that runs inside a window.