After installing OS X as a VM running the Server role, I have noticed excessive CPU usage while idling. I have narrowed this down to the default screensaver which runs on the login page. Even if you disable this screensaver as a user, it will not disable it for the login screen. I have found that the only way to resolve this is to actually delete the screensaver file itself! Here is how to do it.
sudo su
cd "/System/Library/Screen Savers/"
rm -r Flurry.saver/