I have only the base KDE installed (
sudo apt-get install plasma-desktop), not the entire
kubuntu-desktop. Unfortunately GTK apps have the fugly Raleigh theme. I've installed QtCurve with
sudo apt-get install qtcurve, but the GTK apps still have Raleigh theme. I assume I have to select the QtCurve theme somehow.
@13east has posted a picture of the settings dialog in his answer below. Unfortunately the GTK+ appearance is the only tab that is missing from my Settings Dialog. I assume this is because I've installed only plasma-desktop instead of the entire kubuntu-desktop. Is there a way to manually set the theme, perhaps by editing some configuration files?