Uma coisa boa para tentar é remover completamente todos os pacotes do KDE . O comando abaixo é para o Ubuntu 10.10:
sudo apt-get remove akonadi-server akregator amarok amarok-common amarok-utils apport-kde apturl-kde ark bluedevil cdparanoia cdrdao docbook-xsl docbook-xsl-doc-html dolphin dragonplayer gdebi-core gdebi-kde gnupg-agent gnupg2 gtk2-engines-qtcurve gwenview hal hal-info ibus-qt4 icoutils jockey-kde k3b k3b-data kaddressbook kamera kate kcalc kde-config-gtk kde-config-touchpad kde-window-manager kde-zeroconf kdebase-bin kdebase-data kdebase-runtime kdebase-runtime-data kdebase-workspace kdebase-workspace-bin kdebase-workspace-data kdebase-workspace-kgreet-plugins kdegraphics-libs-data kdegraphics-strigi-plugins kdelibs-bin kdelibs5 kdelibs5-data kdelibs5-plugins kdemultimedia-kio-plugins kdepasswd kdepim-groupware kdepim-kresources kdepim-runtime kdepim-strigi-plugins kdepim-wizards kdepimlibs-kio-plugins kdesudo kdm kdoctools kfind khelpcenter4 kinfocenter klipper kmag kmail kmix kmousetool knm-runtime knotes konsole kontact kopete kopete-message-indicator korganizer kpackagekit kppp krdc krfb krosspython ksnapshot ksysguard ksysguardd ksystemlog ktimetracker ktorrent ktorrent-data kubuntu-debug-installer kubuntu-default-settings kubuntu-desktop kubuntu-docs kubuntu-firefox-installer kubuntu-konqueror-shortcuts kubuntu-netbook-default-settings kubuntu-notification-helper kvkbd kwalletmanager language-selector-qt libakonadi-contact4 libakonadi-kabc4 libakonadi-kcal4 libakonadi-kde4 libakonadi-kmime4 libakonadiprivate1 libao-common libao4 libattica0 libaudio2 libbluedevil1 libboost-program-options1.42.0 libcln6 libclucene0ldbl libdbusmenu-qt2 libdebconf-kde0 libdirectfb-1.2-9 libepub0 libflac++6 libgif4 libgpgme++2 libgps19 libhal-storage1 libhal1 libibus-qt1 libilmbase6 libindicate-qt0 libiodbc2 libk3b6 libkabc4 libkatepartinterfaces4 libkblog4 libkcal4 libkcddb4 libkdcraw8 libkde3support4 libkdecorations4 libkdecore5 libkdepim4 libkdesu5 libkdeui5 libkdewebkit5 libkdnssd4 libkephal4 libkexiv2-8 libkfile4 libkholidays4 libkhtml5 libkimap4 libkimproxy4 libkio5 libkipi7 libkjsapi4 libkjsembed4 libkldap4 libkleo4 libkmediaplayer4 libkmime4 libknewstuff2-4 libknewstuff3-4 libknotifyconfig4 libkntlm4 libkonq5 libkonq5-templates libkontactinterface4 libkopete4 libkparts4 libkpgp4 libkpimidentities4 libkpimtextedit4 libkpimutils4 libkpty4 libkresources4 libkrosscore4 libkrossui4 libksba8 libkscreensaver5 libksgrd4 libksieve4 libksignalplotter4 libktexteditor4 libktnef4 libktorrent-l10n libktorrent2 libkunitconversion4 libkutils4 libkwineffects1a libkworkspace4 libkxmlrpcclient4 liblastfm0 libloudmouth1-0 libmailtransport4 libmessagecore4 libmessagelist4 libmicroblog4 libmimelib4 libmng1 libmodplug1 libmpcdec6 libmsn0.3 libmysqlclient16 libnepomuk4 libnepomukquery4a libokularcore1 libopenexr6 libotr2 libpackagekit-glib2-14 libpackagekit-qt-14 libphonon4 libplasma-geolocation-interface4 libplasma3 libplasmaclock4b libplasmagenericshell4 libpolkit-qt-1-0 libpoppler-qt4-3 libprocesscore4a libprocessui4a libqalculate5 libqapt-runtime libqapt1 libqca2 libqca2-plugin-ossl libqgpgme1 libqimageblitz4 libqjson0 libqt4-dbus libqt4-designer libqt4-help libqt4-network libqt4-opengl libqt4-qt3support libqt4-script libqt4-scripttools libqt4-sql libqt4-sql-mysql libqt4-sql-sqlite libqt4-svg libqt4-test libqt4-xml libqt4-xmlpatterns libqtcore4 libqtgui4 libqtscript4-core libqtscript4-gui libqtscript4-network libqtscript4-sql libqtscript4-uitools libqtscript4-xml libqtwebkit4 libreadline5 libsolid4 libsolidcontrol4a libsolidcontrolifaces4 libsoprano4 libssh-4 libstreamanalyzer0 libstreams0 libsyndication4 libtag-extras1 libtaskmanager4a libtelepathy-qt4-0 libthreadweaver4 libts-0.0-0 libvirtodbc0 libvncserver0 libweather-ion4a libxcb-shape0 libxcb-xv0 libxine1 libxine1-bin libxine1-console libxine1-misc-plugins libxine1-x libzip1 mysql-client-core-5.1 mysql-common mysql-server-core-5.1 network-manager-pptp-kde odbcinst odbcinst1debian2 okular okular-extra-backends openoffice.org-kde openoffice.org-style-oxygen oxygen-cursor-theme oxygen-icon-theme oxygen-icon-theme-complete packagekit packagekit-backend-aptcc phonon phonon-backend-xine pinentry-gtk2 pinentry-qt4 plasma-dataengines-addons plasma-dataengines-workspace plasma-desktop plasma-netbook plasma-scriptengine-javascript plasma-scriptengine-python plasma-widget-facebook plasma-widget-folderview plasma-widget-kimpanel plasma-widget-kimpanel-backend-ibus plasma-widget-kubuntu-feedback plasma-widget-menubar plasma-widget-message-indicator plasma-widget-networkmanagement plasma-widget-quickaccess plasma-widgets-addons plasma-widgets-workspace plymouth-theme-kubuntu-logo plymouth-theme-kubuntu-text polkit-kde-1 printer-applet python-kde4 python-packagekit python-qt4 python-qt4-dbus python-sip qapt-batch quassel quassel-data rekonq shared-desktop-ontologies smartdimmer software-properties-kde soprano-daemon system-config-printer-kde systemsettings tsconf ttf-dejavu ttf-dejavu-extra update-manager-kde usb-creator-kde userconfig virtuoso-minimal virtuoso-opensource-6.1-bin virtuoso-opensource-6.1-common && sudo apt-get install ubuntu-desktop
Isso certamente deve alterar seu tema de inicialização de volta. Você pode, no entanto, precisar reinstalar quaisquer programas do KDE, como o Krusader, assim que isso for feito.
Você também pode querer olhar para a pergunta neste site intitulada Redefinir a configuração da fonte gnome?