Some of the dirtiest computers come from some of the cleanest offices. Make any sense? That's because they were placed on the floor (carpeted of course) and left running 24/7/365, and had a vacuum cleaner ran all around them every night for years, leaving them to suck in all the dust stirred up by the vac. If you must put your tower under the desk, on the floor, at least put a board, a brick, anything to raise it up a bit from the carpet.

On the same note, how many IT techs show up at work in full EPA garb? Ripping into a computer from one end to the other, replacing motherboards, net cards, CPUs, memory, power supplies, etc after etc. Maybe the ones at NASA had a space suit placed conveniently nearby, that they could slip in to after morning coffee, donuts, and mars bars