I've also tried to install Ubuntu with no luck. I was following the instructions on (mangled URL because I can't post links) wiki ubuntu Touch Devices wingray
First I installed cm-10.1-20130228-UNOFFICIAL-wingray.zip, which was linked on the page. The Ubuntu version I installed was saucy-preinstalled-phablet-armhf.zip, since the link on the page no longer worked. Afterwards my Xoom only showed a black screen after booting, although I was still able to connect with adb and open a shell. I changed the string in /usr/bin/ubuntu-session using ubuntu_chroot, but it didn't make any difference.
It seems that the CM version was probably the problem - I couldn't get the Xoom to show anything graphically as long as I was using that CM version. I tried installing a few other wingray images from the CyanogenMod dowload page, and they all worked, but when I installed Ubuntu on top of that, I was unable to find a way to boot Ubuntu. In CWM it always seemed that Ubuntu installed fine, and the Xoom booted, but there was no way to start Ubuntu and when I connected with adb, ubuntu_chroot wasn't there.
This was the case no matter what CM version I was using and whether I was using the current Ubuntu version, saucy-preinstalled-phablet-armhf.zip, or the one linked in the thread here (quantal-preinstalled-phablet-armhf-signed.zip). Does anyone know how to start Ubuntu after installing it? Or is it because the CM version is incompatible?