These instructions are for Ubuntu 11.10 on which the Xubuntu Desktop was installed using either the Ubuntu Software Center or sudo apt-get on the command line.
The instructions may be the same for other versions, but no guarantee is made.
When the Xubuntu Desktop is installed in Ubuntu 11.10, it installs several additional packages and libraries. Not all these packages and libraries are uninstalled when you uninstall the Xubuntu Desktop – several packages (like Abiword) do not get uninstalled.
Quick Uninstall
This is not recommended because it will remove all packages installed along with Xubuntu. This may include packages you previously installed (like Abiword).
Note: this uninstall command assumes Xubuntu Desktop was installed on a fresh Ubuntu 11.10.
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 remove --auto-remove abiword abiword-common abiword-plugin-grammar abiword-plugin-mathview bison blueman brltty-x11 catfish elementary-icon-theme exo-utils flex gigolo gimp gimp-data gmusicbrowser gnome-icon-theme-full gnome-system-tools gnome-time-admin gnumeric gnumeric-common gnumeric-doc gstreamer0.10-gnomevfs gthumb gthumb-data gtk2-engines-pixbuf gtk2-engines-xfce indicator-application-gtk2 indicator-messages-gtk2 indicator-sound-gtk2 indicator-status-provider-pidgin leafpad libabiword-2.8 libaiksaurus-1.2-0c2a libaiksaurus-1.2-data libaiksaurusgtk-1.2-0c2a libao-common libao4 libaudio-scrobbler-perl libbabl-0.0-0 libclutter-1.0-0 libclutter-1.0-common libclutter-gtk-1.0-0 libcogl-common libcogl5 libconfig-inifiles-perl libencode-locale-perl libept1 libexo-1-0 libexo-common libexo-helpers libfile-listing-perl libfont-afm-perl libgarcon-1-0 libgarcon-common libgdome2-0 libgdome2-cpp-smart0c2a libgegl-0.0-0 libgimp2.0 libglade2-0 libgnomevfs2-extra libgoffice-0.8-8 libgoffice-0.8-8-common libgsf-1-114 libgsf-1-common libgstreamer-perl libgtk2-notify-perl libgtk2-trayicon-perl libgtkmathview0c2a libhtml-form-perl libhtml-format-perl libhtml-parser-perl libhtml-tagset-perl libhtml-tree-perl libhttp-cookies-perl libhttp-daemon-perl libhttp-date-perl libhttp-message-perl libhttp-negotiate-perl libido-0.1-0 libilmbase6 libio-socket-ssl-perl libjpeg-progs libkeybinder0 liblink-grammar4 libloudmouth1-0 liblwp-mediatypes-perl liblwp-protocol-https-perl libmailtools-perl libnet-dbus-perl libnet-http-perl libnet-ssleay-perl liboobs-1-5 libopenexr6 libotr2 libots0 libpolkit-gtk-1-0 libsexy2 libtagc0 libthunarx-2-0 libtie-ixhash-perl libtimedate-perl libtumbler-1-0 liburi-perl libwv-1.2-3 libwww-perl libwww-robotrules-perl libxfce4ui-1-0 libxfce4util-bin libxfce4util-common libxfce4util4 libxfcegui4-4 libxfconf-0-2 libxml-parser-perl libxml-twig-perl libxml-xpath-perl libxss1 lightdm-gtk-greeter link-grammar-dictionaries-en m4 mpg321 murrine-themes orage parole pastebinit pidgin pidgin-data pidgin-libnotify pidgin-microblog pidgin-otr plymouth-theme-xubuntu-logo plymouth-theme-xubuntu-text python-configobj python-glade2 quadrapassel ristretto screensaver-default-images synaptic system-tools-backends tango-icon-theme tango-icon-theme-common tcl8.5 thunar thunar-archive-plugin thunar-data thunar-media-tags-plugin thunar-volman ttf-droid ttf-lyx tumbler tumbler-common xchat xchat-common xfburn xfce-keyboard-shortcuts xfce4-appfinder xfce4-cpugraph-plugin xfce4-dict xfce4-fsguard-plugin xfce4-indicator-plugin xfce4-mailwatch-plugin xfce4-mixer xfce4-mount-plugin xfce4-netload-plugin xfce4-notes xfce4-notes-plugin xfce4-notifyd xfce4-panel xfce4-places-plugin xfce4-power-manager xfce4-power-manager-data xfce4-quicklauncher-plugin xfce4-screenshooter xfce4-session xfce4-settings xfce4-smartbookmark-plugin xfce4-systemload-plugin xfce4-taskmanager xfce4-terminal xfce4-utils xfce4-verve-plugin xfce4-volumed xfce4-weather-plugin xfconf xfdesktop4 xfdesktop4-data xfwm4 xfwm4-themes xscreensaver xscreensaver-data xscreensaver-gl xubuntu-artwork xubuntu-default-settings xubuntu-desktop xubuntu-docs xubuntu-icon-theme xubuntu-wallpapers
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 allow you to uninstall only the packages that were installed when Xubuntu Desktop was installed. The instructions are generic and work for any installed package.
This involves (1) identifying which packages were installed and (2) creating a command to uninstall only those packages.
This leaves intact any packages you may have installed (like Abiword) instead of blindly assuming that they were installed as part of Xubuntu Desktop.