I don't want to use it at all.
The friend that's having me set this up for him said, and I quote:
"UML is pretty close to full speed (if using the host-kernel modules. It can also run slower in userland) UML effectively sandboxes each server. This is a security benefit in the best sense of the phrase:
It keeps a server from being screwed up by a security hole in another one, a reboot-bug in another one, us having to do something stupid to reinstall another one, or us just screwng up a server."
So there ya go.