I cannot use any GTK themes at all in Xubuntu 13.04. It worked up until I tried to (unsuccessfully) setup 3 monitors.
EDIT: I ran
gtk-window-decorator --replace and got
Window manager warning: Failed to load theme "Adwaita": Failed to find a valid file for theme Adwaita
I do not have Adwaita selected on the appearance GUI, in fact, it is not even an option. Where is it pulling that value from?