My old friend debootstrap threw this error at me when I tried to install 12.04 from within 10.10. Taking a look at /usr/share/debootstrap/scripts, all of the recent Ubuntu’s are just symlinks to gutsy. I added another symlink called precise and pointing at gutsy, and all was well.
I was happy with the Alt-Tab behavior before Unity. I tend to switch windows very rapidly and the attempt to animate things, and I find the distinction between Alt-Tab and Alt-` to be very annoying, especially under certain circumstances when Alt-Tab actually does behave as Alt-` does.
Here are some instructions to fix this. I selected the Static Application Switcher. I have not tried the Shift Application Switcher.