So, looks like the Nexus S can run MeeGo too :o) have a custom kernel going and booted the OS from a rootfs image on the internal memory (didn't have to flash!), but as you can see the display output is fscked (maybe due to the AMOLED?) and the touchscreen isn't working either.
But… I think this is the first non-Android OS running on the Nexus S so far, so thought it was worth a post! Watch this space…
Update: Try it yourself - PROS ONLY
So if you're insane enough, you can try it yourself right now…
You will need to build a MeeGo rootfs first, in ext2 format. Use my kickstart as a base, it has a few niceties like adb support (i.e. the only way you can interact with it right now). With your image successfully compiled, copy it to linux/rootfs.ext2 on your Nexus S' internal memory (completely safe, no flashing required).
My boot.img is here - you will need to use fastboot to boot it (fastboot boot nexuss-meego-boot.img), or you can flash it to recovery if you want to dual boot.
As seen in the photo, you won't really be able to see anything onscreen, but you can use adb to get a root shell like on any Android device. Poke around, play with it, improve upon it, etc. Actually going much further than this is beyond me unless I can find some talented kernel hackers with Nexus S hardware to test on.
Matching XDA-developers thread here.
UPDATE 2: Have modified the kernel to force full brightness on the screen. It's tinted very yellow, so it's not perfect, but you can see better now!
UPDATE 3 - UBUNTU:
Well, this is more of a side note, but Ubuntu runs fine on the Nexus S using the same process. Check the XDA thread for more info.