Ouch! If you are considering upgrading, you might want to give this one a good six months to mature. Of course, Canonical does recommend waiting until 12.04.1 for current LTS users.
But that recommendation wouldn't seem to be to help one avoid the inability to boot and a failure of DNS! For my 64-bit System76 (yep, this is officially supported Ubuntu hardware) Leopard 1 (Intel Core i7), running 'boot-repair' from an amd64 12.04 image on a persistant USB stick created with PenDrive Linux was the first step.
From 'boot-repair', I re-installed grub, and then enabled the master boot record. Updating grub and purging the kernel list was not possible. Then I booted into recovery mode, re-installed grub, and did a 'sudo dpkg --configure -a'. Boot failed again on reboot into normal mode. So I repeated the 'boot-repair' steps, running from the USB stick.
Several more boots proved the system stable. Then on to the joy of no domain name lookup! 'sudo apt-get remove resolvconf' solved that. But first, I had to add certain privileges to my user to be able to run that successfully. This is odd since it worked earlier from outside Gnome, from the recovery mode command prompt.
Overall, it's very surprising to see such a rough upgrade situation from Ubuntu. This is how Ubuntu used to always be six years ago, but I thought things were getting better. If you're ready to not have your computer for a couple days, upgrade to 12.04! :) Or give it six months to a year so that these issues can be resolved more easily.