The only boards that could possibly take ubuntu on nand are the mini210S 4GB MLC nand boards. However, superboot cannot burn images > 2GB, when you convert the server or desktop version of ubuntu to yaffs2 image, it's 2.1GB.
There is another solution, run ubuntu from an SD card make sure you have the ubuntu-desktop or server tarball on the SD card too, once booted, you can mount the system partition to a temporary folder from a console:
sudo mount /dev/mtdblock4 /mnt
You can then do:
sudo rm -rf /mnt/*
then you can do:
sudo tar xzvf ubuntu-desktop-1204_20120628.tgz -C mnt/ --strip-components=1
after that you should be able to use a normal nand based kernel with the usual linux command line for booting from nand.
I hope that helps someone :-)
