Try to keep your computer in a relatively dust-free part of the house. It's amazing how much the ambiant dust in the air contributes to build-up in the computer. I have two cats, and when my machines were near their boxes, the dust from the litter would build up to 1/16" in a month. Made them smell good...but also built up heat and grit. I had to vacuum them out and wipe them down with a damp anti-static cloth weekly. Moving the boxes made a big difference. Also, simple things like changing the filter in your heating/cooling system reduces dust, as does a good dirt-capture vacuum sytem.