The Ubuntu image used is the HD2 Ubuntu image (v 0.3), loaded from a file on the internal memory (again, no flashing required - you can thank me later).
The touchscreen isn't yet working, but that's my kernel at fault. Will fix that with the MeeGo stuff.
If you want to try this yourself, first grab yourself a copy of Ubuntu for HD2, and take just the rootfs.ext2 file and drag it to your Nexus S (put it in a folder called 'ubuntu' - lowercase is important!).
Then use fastboot to boot the following image (or flash it to recovery partition if you're daring and know how dangerous that can be):
You will need to do one minor edit once the device is booted; you will see the screen output is very weird; ADB push the following file to /etc/X11/xorg.conf, and then reboot Ubuntu:
If you're in any way interested, please click the thanks button! Otherwise, enjoy!