Great introduction and tutorial about lguest from Rusty Russels at Linux.conf.au 2008 today (thursday). Lguest (former "lhype") is a very fast and lightweight virtualization approach which concentrates on "running Linux on Linux". New lguests vms are started by a lguest launcher util which basically reserves a specifc memory region in the Host kernel and then re-maps the (l)guests hypercalls.
The lguest tutorial provided a ready prepared Qemu filesystem so the participants could bring up their own lguest-Hosts easy and start hacking on the the different tutorial tasks. What a fun. Even myself was able to implement a new hypercall printing out some string on the lguest console at startup (and i do not consider myself a kernel-hacker).
Lguest is definitely an interesting project and i am curious how it will find its place along the other available virtualization technologies used today.