If you have seen the inner side of a PowerMac G5, you probably have noticed the plethora of fans inside. If the G5 was powered and showcased, chances are that you've seen them spinning slowly and quietly.
Most of the time, the G5 is a very silent machine. But when you unleash the beast, especially a dual processor one, you cannot ignore it anymore. The processors fan speed is proportional to their instant load, and you can quite easily spot when the machine is fully busy crunching your precious bits of data without resorting to graphical tools such as the Activity Monitor.
An interesting side effect is to pinpoint peculiar processor-hungry tasks. When I'm compressing hours of videos through QuickTime, it's rather normal to hear the fans. But is it when I'm just looking at an HTML email or simply clicking on the scroll bar in Microsoft Entourage? Believe it or not, just maintaining the mouse click on a scroll bar or leaving an HTML email on screen (not just rendering it) requires megaflops of super-computer power for Entourage to handle.
It's the most expensive whistle-blower for bad code I've ever had.