Every now and then I'd like to play with a fresh minimal install of Ubuntu (to test sysadminish scripts, application install instructions, package dependency lists etc.).

I'd like to have a tool as simple to use as testdrive: pick a version (say, 'maverick'), run a command, get a shell in a new virtual machine.

I'd like that shell to be in the current terminal, rather than a new GUI window that testdrive uses. Setting up the new VM to accept SSH logins with my ssh public key is fine.

I'd like the VM to have network access out of the box; NAT to a virtual network interface is fine.

Why a VM? Chroots don't really cut it: installing, say, Apache in a chroot would fail because it would try to listen on port 80, which is already taken. Containers might work, though, if there are any that are supported by standard Ubuntu kernels.