When GNOME is installed in Ubuntu 12.04, it installs several packages and libraries it requires as well as some optional packages. Not all these packages and libraries are uninstalled when you uninstall GNOME. Several packages (like epiphany-browser and gnuchess) do not get uninstalled.

Quick Uninstall

1) Open a terminal (instructions can be found here).

2) Enter the following command (it is very long and a single line):

sudo apt-get purge --auto-remove alacarte bogofilter bogofilter-bdb bogofilter-common browser-plugin-gnash cheese  cheese-common cups-pk-helper dconf-tools desktop-base ekiga epiphany-browser  epiphany-browser-data epiphany-extensions evolution evolution-common  evolution-plugins evolution-webcal fonts-cantarell gdebi gdebi-core gdm  gedit-plugins gimp gimp-data gir1.2-accountsservice-1.0 gir1.2-caribou-1.0  gir1.2-clutter-1.0 gir1.2-cogl-1.0 gir1.2-coglpango-1.0 gir1.2-folks-0.6  gir1.2-gdesktopenums-3.0 gir1.2-gee-1.0 gir1.2-gjsdbus-1.0 gir1.2-gkbd-3.0  gir1.2-gucharmap-2.90 gir1.2-json-1.0 gir1.2-mutter-3.0  gir1.2-networkmanager-1.0 gir1.2-panelapplet-4.0 gir1.2-polkit-1.0  gir1.2-telepathyglib-0.12 gir1.2-telepathylogger-0.2 gir1.2-upowerglib-1.0  gir1.2-xkl-1.0 gjs glchess glines gnash gnash-common gnect gnibbles gnobots2  gnome gnome-applets gnome-applets-data gnome-backgrounds gnome-contacts  gnome-core gnome-dictionary gnome-games gnome-games-extra-data  gnome-icon-theme-extras gnome-icon-theme-full gnome-js-common gnome-panel  gnome-panel-data gnome-session-fallback gnome-shell gnome-shell-common  gnome-themes-standard gnome-video-effects gnotravex gnotski gnuchess  gnuchess-book gtali hamster-applet iagno imagemagick imagemagick-common  indicator-applet-complete inkscape libbabl-0.0-0 libblas3gf libbonobo2-0  libbonobo2-common libbonoboui2-0 libbonoboui2-common libboost-iostreams1.46.1  libboost-program-options1.46.1 libboost-signals1.46.1 libboost-thread1.46.1  libcapi20-3 libcaribou-common libcaribou0 libcdt4 libcheese-gtk21 libcheese3  libclutter-1.0-0 libclutter-1.0-common libclutter-gst-1.0-0 libclutter-gtk-1.0-0  libclutter-imcontext-0.1-0 libcluttergesture-0.0.2-0 libcogl-common  libcogl-pango0 libcogl9 libept1.4.12 libevolution libgc1c2 libgdict-1.0-6  libgdict-common libgegl-0.0-0 libgfortran3 libgimp2.0 libgjs0c libglade2-0  libgnome2-0 libgnomecanvas2-0 libgnomecanvas2-common libgnomeui-0  libgnomeui-common libgnomevfs2-extra libgraph4 libgsl0ldbl libgtkhtml-4.0-0  libgtkhtml-4.0-common libgtkhtml-editor-4.0-0 libgtkmm-2.4-1c2a libgvc5  libilmbase6 liblapack3gf liblqr-1-0 libmagick++4 libmagickcore4  libmagickcore4-extra libmagickwand4 libmozjs185-1.0 libmusicbrainz4-3 libmutter0  libmx-1.0-2 libnetpbm10 libodbc1 libopal3.10.2 libopenexr6 libpanel-applet--0  libpathplan4 libpst4 libpt2.10.2 libseed-gtk3-0 libwmf-bin liferea liferea-data  lightsoff menu menu-xdg mutter-common netpbm notification-daemon odbcinst  odbcinst1debian2 perlmagick python-gmenu python-gnome2 python-lxml python-numpy  python-pyorbit python-uniconvertor quadrapassel sound-juicer swell-foop synaptic  unixodbc

It is easiest to copy the line and paste it into the terminal (right-click on the terminal and select Paste from the popup menu).

Preferred Uninstall

The better way to uninstall it is to follow the directions on this page.

This will show you on how to uninstall only the packages that were installed when GNOME was installed. The instructions are generic and work for any installed package.

It involves:

1. identifying which packages were installed and
2. creating a command to uninstall only those packages

It leaves intact any packages you may have installed (like epiphany-browser or gnuchess) or that were installed by other packages instead of blindly assuming that they were installed along with GNOME.