http://www.psychocats.net/ubuntu/puregnome

Note, this applies only to Ubuntu 11.10 (Oneiric)

If you are using kubuntu or xubuntu, check for purekubuntu/xubuntu entries.

sudo apt-get remove abiword abiword-common abiword-plugin-grammar abiword-plugin-mathview ace-of-penguins audacious audacious-plugins chromium-browser chromium-browser-l10n chromium-codecs-ffmpeg elementary-icon-theme esound-common galculator gdebi gdebi-core giblib1 gnome-icon-theme-full gnome-mplayer gnome-system-tools gnome-time-admin gnumeric gnumeric-common gnumeric-doc gpicview gtk2-engines-pixbuf guvcview hardinfo indicator-status-provider-pidgin leafpad libabiword-2.8 libaiksaurus-1.2-0c2a libaiksaurus-1.2-data libaiksaurusgtk-1.2-0c2a libaudclient2 libaudcore1 libaudiofile0 libavcodec53 libavformat53 libavutil51 libbinio1ldbl libcddb2 libcompfaceg1 libcue1 libdca0 libdirectfb-1.2-9 libdiscid0 libdvdnav4 libdvdread4 libenca0 libencode-locale-perl libept1 libesd0 libexo-1-0 libexo-common libfaad2 libfile-listing-perl libfluidsynth1 libfm-data libfm-gtk-data libfm-gtk1 libfm1 libfont-afm-perl libgdome2-0 libgdome2-cpp-smart0c2a libglade2-0 libgoffice-0.8-8 libgoffice-0.8-8-common libgringotts2 libgsf-1-114 libgsf-1-common libgsm1 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 libid3tag0 libimlib2 libio-socket-ssl-perl libjpeg-progs liblink-grammar4 libloudmouth1-0 liblwp-mediatypes-perl liblwp-protocol-https-perl libmailtools-perl libmcrypt4 libmcs1 libmenu-cache1 libmms0 libmowgli2 libmusicbrainz3-6 libnet-dbus-perl libnet-http-perl libnet-ssleay-perl libobrender27 libobt0 libonig2 liboobs-1-5 libopenal1 libopts25 libots0 libpisock9 libpolkit-gtk-1-0 libpostproc52 libresid-builder0c2a libschroedinger-1.0-0 libsidplay2 libsvga1 libswscale2 libtar0 libtie-ixhash-perl libtimedate-perl libts-0.0-0 libuniconf4.6 liburi-perl libva1 libvdpau1 libvpx0 libwebcam0 libwv-1.2-3 libwvstreams4.6-base libwvstreams4.6-extras 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 libxvidcore4 link-grammar-dictionaries-en lm-sensors lubuntu-artwork lubuntu-core lubuntu-default-settings lubuntu-desktop lubuntu-icon-theme lxappearance lxappearance-obconf lxde-common lxde-core lxdm lxinput lxkeymap lxlauncher lxmenu-data lxpanel lxpanel-indicator-applet-plugin lxrandr lxsession lxsession-edit lxshortcut lxtask lxterminal mplayer mtpaint ntp obconf openbox openbox-themes osmo pcmanfm pidgin pidgin-data pidgin-libnotify pidgin-microblog plymouth-theme-lubuntu-logo plymouth-theme-lubuntu-text scrot sylpheed sylpheed-doc sylpheed-i18n sylpheed-plugins synaptic system-tools-backends transmission tsconf ttf-lyx uvcdynctrl uvcdynctrl-data wvdial xfburn xfce-keyboard-shortcuts xfce4-power-manager xfce4-power-manager-data xfconf xfonts-100dpi xpad xscreensaver xscreensaver-data && sudo apt-get install ubuntu-desktop

For Ubuntu 13.04 Use this command

sudo apt-get remove abiword abiword-common abiword-plugin-grammar abiword-plugin-mathview ace-of-penguins audacious audacious-plugins chromium-browser chromium-browser-l10n chromium-codecs-ffmpeg elementary-icon-theme esound-common galculator gdebi gdebi-core giblib1 gnome-icon-theme-full gnome-mplayer gnome-system-tools gnome-time-admin gnumeric gnumeric-common gnumeric-doc gpicview gtk2-engines-pixbuf guvcview hardinfo indicator-status-provider-pidgin leafpad libabiword-2.9 libaiksaurus-1.2-0c2a libaiksaurus-1.2-data libaiksaurusgtk-1.2-0c2a libaudclient2 libaudcore1 libaudiofile1 libavcodec53 libavformat53 libavutil51 libbinio1ldbl libcddb2 libcompfaceg1 libcue1 libdca0 libdirectfb-1.2-9 libdiscid0 libdvdnav4 libdvdread4 libenca0 libencode-locale-perl libept1.4.12 libesd0 libexo-1-0 libexo-common libfaad2 libfile-listing-perl libfluidsynth1 libfm-data libfm-gtk-data libfm-gtk3 libfm3 libfont-afm-perl libgdome2-0 libgdome2-cpp-smart0c2a libglade2-0 libgoffice-0.8-8 libgoffice-0.8-8-common libgringotts2 libgsf-1-114 libgsf-1-common libgsm1 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 libid3tag0 libimlib2 libio-socket-ssl-perl libjpeg-progs liblink-grammar4 libloudmouth1-0 liblwp-mediatypes-perl liblwp-protocol-https-perl libmailtools-perl libmcrypt4 libmcs1 libmenu-cache2 libmms0 libmowgli2 libmusicbrainz3-6 libnet-dbus-perl libnet-http-perl libnet-ssleay-perl libobrender27 libobt0 libonig2 liboobs-1-5 libopenal1 libopts25 libots0 libpisock9 libpolkit-gtk-1-0 libpostproc52 libresid-builder0c2a libschroedinger-1.0-0 libsidplay2 libsvga1 libswscale2 libtar0 libtie-ixhash-perl libtimedate-perl libts-0.0-0 libuniconf4.6 liburi-perl libva1 libvdpau1 libvpx1 libwebcam0 libwv-1.2-4 libwvstreams4.6-base libwvstreams4.6-extras 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 libxvidcore4 link-grammar-dictionaries-en lm-sensors lubuntu-artwork lubuntu-core lubuntu-default-settings lubuntu-desktop lubuntu-icon-theme lxappearance lxappearance-obconf lxde-common lxde-core lxdm lxinput lxkeymap lxlauncher lxmenu-data lxpanel lxpanel-indicator-applet-plugin lxrandr lxsession lxsession-edit lxshortcut lxtask lxterminal mplayer mtpaint ntp obconf openbox openbox-themes osmo pcmanfm pidgin pidgin-data pidgin-libnotify pidgin-microblog plymouth-theme-lubuntu-logo plymouth-theme-lubuntu-text scrot sylpheed sylpheed-doc sylpheed-i18n sylpheed-plugins synaptic system-tools-backends transmission tsconf ttf-lyx uvcdynctrl uvcdynctrl-data wvdial xfburn xfce-keyboard-shortcuts xfce4-power-manager xfce4-power-manager-data xfconf xfonts-100dpi xpad xscreensaver xscreensaver-data && sudo apt-get install ubuntu-desktop