You can still use it on the classical Gnome desktop too, and once installed, it'll let you control various CPU related functions such as frequency changing and switching between different power modes on the fly with ease as well.
So, if you run Ubuntu 11.04 or 10.10 and need to give it a try, then open your Terminal and issue the below command...
sudo add-apt-repository ppa:artfwo/ppa
sudo apt-get update
sudo apt-get install indicator-cpufreq