Com base nas respostas anteriores:
Para 11.10
#!/bin/bash
if [ "$XDG_CURRENT_DESKTOP" = "Unity" ]
then
gsettings set org.gnome.desktop.interface gtk-theme 'Ambiance'
gconftool-2 --set --type string /apps/metacity/general/theme 'Ambiance'
gsettings set org.gnome.desktop.interface icon-theme 'Faenza-Ambiance'
else
gsettings set org.gnome.desktop.interface gtk-theme 'Adwaita'
gconftool-2 --set --type string /apps/metacity/general/theme 'Adwaita'
gsettings set org.gnome.desktop.interface icon-theme 'Faenza'
fi
Para 12.04 e 12.10
#!/bin/bash
if [ "$XDG_CURRENT_DESKTOP" = "Unity" ]
then
gsettings set org.gnome.desktop.interface gtk-theme 'Ambiance'
gsettings set org.gnome.desktop.interface icon-theme 'ubuntu-mono-dark'
gsettings set org.gnome.desktop.wm.preferences theme 'Ambiance'
else
gsettings set org.gnome.desktop.interface gtk-theme 'Adwaita'
gsettings set org.gnome.desktop.interface icon-theme 'gnome'
gsettings set org.gnome.desktop.wm.preferences theme 'Adwaita'
fi
Adicione este script a Startup Applications
(Adicionar => Comando sh path/to/script
).