remove the ubuntu-desktop package

This only applies to Oneric 11.10

These removal commands were created based on what Ubuntu, Kubuntu, etc. packages were added to a default Lubuntu installation. It's possible that the commands might remove some other packages you have since added to the default and want to keep. If that's the case, keep track of which packages those are and reinstall them. Your settings should still be there.

sudo apt-get remove acpi-support acpid adium-theme-ubuntu aisleriot apg app-install-data app-install-data-partner appmenu-gtk appmenu-gtk3 appmenu-qt apt-xapian-index apturl apturl-common at-spi2-core avahi-autoipd bamfdaemon banshee banshee-extension-soundmenu banshee-extension-ubuntuonemusicstore baobab binfmt-support bluez-alsa bluez-cups bluez-gstreamer branding-ubuntu brasero brasero-cdrkit brasero-common brltty c2esp checkbox checkbox-gtk cli-common compiz compiz-core compiz-gnome compiz-plugins-default compiz-plugins-main-default compizconfig-backend-gconf cups-bsd dc deja-dup dmz-cursor-theme doc-base duplicity dvd+rw-tools empathy empathy-common eog espeak espeak-data evolution-data-server evolution-data-server-common example-content exiv2 firefox firefox-globalmenu firefox-gnome-support foo2zjs gamin gbrainy gcalctool gcc gcc-4.6 gedit gedit-common geoclue geoclue-ubuntu-geoip ghostscript-x ginn gir1.2-atspi-2.0 gir1.2-gconf-2.0 gir1.2-gmenu-3.0 gir1.2-gtksource-3.0 gir1.2-indicate-0.6 gir1.2-launchpad-integration-3.0 gir1.2-peas-1.0 gir1.2-totem-1.0 gir1.2-totem-plparser-1.0 gir1.2-wnck-3.0 gnome-accessibility-themes gnome-codec-install gnome-control-center gnome-control-center-data gnome-desktop3-data gnome-font-viewer gnome-games-common gnome-icon-theme-symbolic gnome-mahjongg gnome-media gnome-menus gnome-nettool gnome-online-accounts gnome-orca gnome-power-manager gnome-screensaver gnome-screenshot gnome-search-tool gnome-session gnome-session-bin gnome-session-canberra gnome-session-common gnome-settings-daemon gnome-sudoku gnome-system-log gnome-system-monitor gnome-terminal gnome-terminal-data gnome-utils-common gnomine growisofs gstreamer0.10-alsa gstreamer0.10-gconf gstreamer0.10-plugins-base-apps gstreamer0.10-pulseaudio gstreamer0.10-tools guile-1.8-libs gwibber gwibber-service gwibber-service-facebook gwibber-service-identica gwibber-service-twitter hplip hplip-cups hplip-data hwdata ibus ibus-gtk ibus-gtk3 ibus-pinyin ibus-pinyin-db-android ibus-pinyin-db-open-phrase ibus-table im-switch indicator-appmenu indicator-datetime indicator-power indicator-session indicator-sound inputattach intel-gpu-tools kerneloops-daemon lftp libappindicator0.1-cil libasound2-plugins libatk-adaptor libatspi2.0-0 libavahi-gobject0 libbamf0 libbamf3-0 libboost-serialization1.46.1 libbrasero-media3-1 libbrlapi0.5 libc-dev-bin libc6-dev libcamel-1.2-29 libcanberra-pulse libcompizconfig0 libcrypt-passwdmd5-perl libdbus-glib1.0-cil libdbus1.0-cil libdbusmenu-qt2 libdconf-dbus-1-0 libdconf-qt0 libdconf0 libdecoration0 libdotconf1.0 libebackend-1.2-1 libebook1.2-12 libecal1.2-10 libedata-book-1.2-11 libedata-cal-1.2-13 libedataserver1.2-15 libedataserverui-3.0-1 libespeak1 libexempi3 libexiv2-10 libfile-copy-recursive-perl libfolks-telepathy25 libfolks25 libgail-3-common libgail-common libgamin0 libgconf2.0-cil libgd2-xpm libgdata-common libgdata1.7-cil libgdata13 libgdiplus libgeoclue0 libgexiv2-0 libgkeyfile1.0-cil libglew1.5 libglewmx1.5 libglib2.0-bin libglib2.0-cil libglib2.0-data libgmime-2.4-2 libgmime2.4-cil libgnome-control-center1 libgnome-desktop-3-2 libgnome-media-profiles-3.0-0 libgnome-menu-3-0 libgnome-menu2 libgnome2-common libgnomekbd-common libgnomekbd7 libgnomevfs2-0 libgnomevfs2-common libgoa-1.0-0 libgomp1 libgtk-sharp-beans-cil libgtk-vnc-2.0-0 libgtk2.0-cil libgtkmm-3.0-1 libgtksourceview-3.0-0 libgtksourceview-3.0-common libgtkspell3-0 libgudev1.0-cil libgvnc-1.0-0 libgweather-3-0 libgweather-common libgwibber-gtk2 libgwibber2 libhyphen0 libibus-1.0-0 libidl0 libido3-0.1-0 libjson-glib-1.0-0 liblaunchpad-integration1.0-cil liblightdm-gobject-1-0 liblouis-data liblouis2 libmetacity-private0 libmission-control-plugins0 libmng1 libmono-addins-gui0.2-cil libmono-addins0.2-cil libmono-cairo4.0-cil libmono-corlib4.0-cil libmono-csharp4.0-cil libmono-i18n-west4.0-cil libmono-i18n4.0-cil libmono-posix4.0-cil libmono-security4.0-cil libmono-sharpzip4.84-cil libmono-system-configuration4.0-cil libmono-system-core4.0-cil libmono-system-drawing4.0-cil libmono-system-security4.0-cil libmono-system-xml4.0-cil libmono-system4.0-cil libmono-zeroconf1.0-cil libmysqlclient16 libmythes-1.2-0 libnotify-bin libnotify0.4-cil libnux-1.0-0 libnux-1.0-common liboauth0 libopencc1 liborbit2 liboverlay-scrollbar-0.2-0 liboverlay-scrollbar3-0.2-0 libpeas-1.0-0 libpeas-common libprotobuf7 libprotoc7 libpulse-mainloop-glib0 libqt4-dbus libqt4-declarative libqt4-network libqt4-opengl libqt4-script libqt4-sql libqt4-sql-mysql libqt4-svg libqt4-xml libqt4-xmlpatterns libqtbamf1 libqtcore4 libqtdee2 libqtgconf1 libqtgui4 libquadmath0 libquvi0 libraptor2-0 librasqal3 librdf0 libreoffice-base-core libreoffice-calc libreoffice-common libreoffice-core libreoffice-draw libreoffice-emailmerge libreoffice-gnome libreoffice-gtk libreoffice-help-en-us libreoffice-impress libreoffice-math libreoffice-style-human libreoffice-writer librest-0.7-0 librsync1 libsane-hpaio libsdl1.2debian-pulseaudio libspeechd2 libspeexdsp1 libstlport4.6ldbl libsyncdaemon-1.0-1 libtaglib2.0-cil libtelepathy-farsight0 libtelepathy-logger2 libtextcat-data libtextcat0 libtotem-plparser17 libtotem0 libubuntuone-1.0-1 libubuntuone1.0-cil libunique-1.0-0 libunity-2d-private0 libunity-core-4.0-4 libunity-misc4 libutempter0 libuuid-perl libwmf0.2-7-gtk libwnck-3-0 libwnck-3-common libwnck-common libwnck22 libxp6 libxres1 libyajl1 libyaml-tiny-perl libzeitgeist-1.0-1 light-themes lightdm linux-libc-dev make media-player-info metacity metacity-common mono-4.0-gac mono-gac mono-runtime mousetweaks mscompress mysql-common nautilus nautilus-sendto nautilus-sendto-empathy nautilus-share notify-osd notify-osd-icons nux-tools onboard oneconf openprinting-ppds overlay-scrollbar pinyin-database pkg-config plymouth-theme-ubuntu-logo protobuf-compiler ptouch-driver pulseaudio pulseaudio-esound-compat pulseaudio-module-bluetooth pulseaudio-module-gconf pulseaudio-module-x11 pulseaudio-utils pxljr python-brlapi python-configglue python-dateutil python-egenix-mxdatetime python-egenix-mxtools python-farsight python-gconf python-ibus python-imaging python-indicate python-libproxy python-louis python-openssl python-pam python-papyon python-pexpect python-piston-mini-client python-protobuf python-pyatspi2 python-pyinotify python-serial python-speechd python-telepathy python-twisted-bin python-twisted-core python-twisted-names python-twisted-web python-ubuntuone-client python-ubuntuone-control-panel python-ubuntuone-storageprotocol python-uno python-virtkey python-webkit python-wnck qdbus qt-at-spi radeontool rastertosag-gdi rdesktop rfkill rtkit sane-utils seahorse shotwell sni-qt software-center speech-dispatcher splix ssh-askpass-gnome syslinux syslinux-common telepathy-butterfly telepathy-gabble telepathy-haze telepathy-idle telepathy-indicator telepathy-logger telepathy-mission-control-5 telepathy-salut thunderbird thunderbird-globalmenu thunderbird-gnome-support tomboy toshset totem totem-common totem-mozilla totem-plugins ttf-opensymbol ubufox ubuntu-artwork ubuntu-desktop ubuntu-docs ubuntu-mono ubuntu-sounds ubuntu-sso-client ubuntu-system-service ubuntu-wallpapers ubuntuone-client ubuntuone-client-gnome ubuntuone-control-panel ubuntuone-control-panel-gtk ubuntuone-couch ubuntuone-installer unity unity-2d unity-2d-launcher unity-2d-panel unity-2d-places unity-2d-spread unity-asset-pool unity-common unity-greeter unity-lens-applications unity-lens-files unity-lens-music unity-scope-musicstores unity-services uno-libs3 update-inetd ure usb-creator-common usb-creator-gtk vinagre vino whois wodim xbitmaps xcursor-themes xdg-user-dirs-gtk xdiagnose xfonts-mathml xterm xul-ext-ubufox zeitgeist zeitgeist-core zeitgeist-datahub zeitgeist-extension-fts zenity zenity-common && sudo apt-get install lubuntu-desktop

Reference

Getting Back to a Pure LXDE on Ubuntu