So, I have a barebones version of MeeGo (barely) running on the Nexus S. I can't really do much with it on my own, but I'm posting the info here so you can build it and try it for yourself.
• ADB root shell • X11 & UI apps
What doesn't work currently:
• Touchscreen • Super-AMOLED brightness control (screen looks near pitch black) • WiFi • Anything else :-P
If you've never built a MeeGo rootfs before, it's relatively straightforward, and all the binaries are precompiled for you (but it's definitely for developers only).
I have my boot.img (kernel + ramdisk) and a MeeGo kickstart file at http://blog.steventroughtonsmith.com/2011/01/nexus-s-meego.html; you can use fastboot to boot the image, or flash it to the recovery partition to dual boot. The actual MeeGo rootfs is run from a rootfs.ext2 file you can drop onto the Nexus S using Mass Storage mode - no need for messy flashing or the like, you can thank me later).
There's not much else I can do on my own right now, so if you want to see anything become of this do get involved!
My kernel is stock git://android.git.kernel.org/kernel/samsung.git ; make herring_defconfig; the only change was modifying the .config to turn on CONFIG_VT (needed for X11).