In the unlikely even that you’re running OS X on a G4 PowerBook, with a busted display, and only VNC in once every while (because, say, you’re using it as a server), then Apple have included a handy feature for you.
When the Software Update finds something new, it displays a list of available updates. It also bumps the CPU usage, and causes the fan to kick in. When I’m running heavy Tomcat/MySQL apps on the machine it doesn’t sweat as much. So it begs the question, just what the hell is Software Update code doing to use so much CPU to display a static list and wait for user input?
The mind boggles