I have upgraded from Ubuntu 12.04 to 14.04.1
After upgrading Ubuntu-Tweak-Tool as not working as expected.
The tweak setting is not displaying anything.
Screenshot is as:
There in option showing under Appearance, Startup, Desktop, etc.
First Remove Old Ubuntu Tweak using following command in terminal ( Ctrl+Alt+T) .
sudo apt-get purge ubuntu-tweak
Download new Ubuntu Tweak debian package for trusty (current it's ubuntu-tweak_0.8.7-1~trusty2_all.deb ) from http://ubuntu-tweak.com/.
Type following command in terminal
sudo dpkg -i Downloads/ubuntu-tweak_0.8.7-1~trusty2_all.deb