If you've installed *ubuntu-desktop packages to try out Ubuntu's various desktop flavors, you might suddenly find it's not so simple to remove those packages later.
For convenience, we install the *ubuntu-desktop meta-package which pulls in a lot of other packages which make up said desktop (eg., kubuntu-desktop installs various packages specific to the KDE desktop).
If you decide it's not for you, you might think a simple removal of the meta-package will remove everything for you. It doesn't. The following commands will not do what you might think it does.
~$ sudo apt-get purge kubuntu-desktop
~$ sudo apt-get autoremove
All you'll be uninstalling is the kubuntu-desktop meta-package only. The various packages it pulled in that make up the Kubuntu desktop won't get removed along with it. It's how meta-packages work. It's how you can customise your desktop without breaking it when upgrading later. Likewise, autoremove merely removes any orphaned packages but those may or may not include Kubuntu specific packages.
If you really want to remove all those other packages you can copy and paste the terminal commands found here. Some packages that weren't part of the default Ubuntu desktop might get removed so you'll need to reinstall them afterwards though (I had to reinstall GnuCash and Wine, for example).