Here’s a quick off-topic post just to get this Gutsy fix published and easily found on Google, etc.
For some people, opening the Appearance Preferences dialog causes the application to freeze. This program is also known as gnome-appearance-properties.
The freeze usually occurs when trying to switch to another tab, such as the Visual Effects tab, or the Fonts tab. If you are trying to switch to the Visual effects tab and the window keeps freezing, or does nothing at all, this is the post for you.
Users with this problem will find that clicking on the Background tab does nothing :
And that clicking on anything else, such as the Customize theme button, causes a blank or empty window to appear, like so:
Luckily the fix is easy. The offending program is one gtk-qt-engine. This is an optional and apparently not very useful package which tries to help KDE programs run and look better on Gnome. If you want to regain control of your Appearance Preferences screen, you need to remove it :
sudo apt-get remove gtk-qt-engine
Now go to System > Preferences > Appearance and viola! You can now freely modify the look and feel of your system.
We were also able to run all of our favorite KDE programs just fine without the additional help from gtk-qt-engine.