This has happened a few times in the last three years. Hence we are sure of this.
Because of dust buildup the CPU or GPU in some notebook computers gets hotter than usual. E.g. the GPU could be around 72°C instead of around 59°C. You may hear the fan spin faster and louder.
Simple software runs just fine. But…
if you are doing something which uses the processing units, e.g. watching a video stream, everything on the computer becomes horribly slow, really slow, behaves as if less than 10% of the processor is all it has, almost not workable, video stutters, other virtual machines are very slow, may take a minute to close a window, and takes a long time to recover even if you finally can stop the video playback or close one virtual machine.
This apparently isn’t just the effect of the processor protecting itself from overheating, and slowing down from 2.5GHz to 1.6GHz.
We have observed it on Enterprise Linux 6.x to 6.3 versions hosting VMware Workstation 7.x to 9.0.1 versions running Windows XP SP3 virtual machines with current VMware Tools installed.
Last week it has happened, again, on a high-end Dell Precision M6400 with quad-core and an Nvidia Quadro FX 3700M.
The problem went away when using a vacuum cleaner to suck dust out of the notebook’s air intake slots at the bottom of the notebook computer, both on the left and on the right, while the computer was running.