So I installed the cinnamon desktop environment on Ubuntu 12.10 but now I want to uninstall it. What would the command line(s) be to uninstall it?
In order to remove cinnamon and all the related packages the PPA installed you need first to install PPA-purge: disables a PPA and reverts to official packages.
sudo apt-get install ppa-purge && sudo ppa-purge ppa:gwendal-lebihan-dev/cinnamon-stable
You can see a little example of how to use PPA-purge http://www.webupd8.org/2009/12/remove-ppa-repositories-via-command.html