Getting good dust filter grills and aluminum mesh or steel mesh filter , is a lot easier than it was before. http://www.xtremesystems.org/forums/showthread.php?209801-Some-Wire-Mesh-Filter-Fan-Grill-Testing... . Specifically not this type http://www.performance-pcs.com/catalog/index.php?main_page=popup_image_scroll&products_id=2334&image_scroll_id=0 a filter Mesh not a "Grill"
I have always applied filtering methods in my computers, because of how many wires I have connected to them, it is difficult to just Pull it and take it outside to use the compressor on it. Canned air, and vaccumes are almost useless.
When filtered the flow is reduced, there is not a filter method to date that does not reduce the air flow some, and the filters have to be properly maintanced. Because of that it is nice to have them easily accessable and not stuffed in the case. . At first the temperatures of the computer can be higher , or require more fan speed in thermal control situations. In the Long term (years) the filtered computer Maintains its temperature much better, because of the lack of internal dust buildup. Eventually the computer still has to be cleaned anyway, about 1/4 as often.
Some of the "Foams" that we got in fan grill items broke down over time (about 4-5 years). Plastic meshes are terrible for air flow, cloth type meshes lasted longer but are not as free flowing as foams. The newest aluminum and steel meshes they are comming out with are less restriction , and longer lasting. Any Metal meshes should be mostly Air, not metal. My favorite DIY is the foam from the top of a Shop-Vac , the filter foam that is used when doing wet work. it allows for very free flow, stops all large dust particles, lasts time, cleans easily, and comes in a size that can have some good coverages, and available locally.