i may be way of mark, but the UML do not make the kernel think its running directly on the hardware, but the lguest behaves like a virtualization system.

hmm, i wonder, can it manage to freeze the state of the guest system? and if so, how hard would it be to build some systems around it that loads the guest from a usb stick so that you can in theory bring your desktop with you and not even requiring to reboot?