If you have filters the dust inside the case and on the inside part of the window will not be too bad. Make sure to get a filter preferably aluminum mesh for the window, the front intake already has a filter. As for the outside of the window, I am in a dorm which is extremely dusty. I tend to dust everything about once a week. After 1 week of dust, I can write my name in my television. The dust on the window is really not bad at all. I guess it all depends on how anal you are.
Brian