Case Fans: Blowing & Sucking?
 

I was doing my annual computer maintenance and am getting concerned about the amount of dust and crud building up in my case. Besides a 2 fan power supply I have the vid card fan and 2 case fans. The case fan in the front sucks in air (and dust) and the one in the back blows out. Would it be better to have both case fans blow out and possibly cut down on the dust or am I getting better cooling by moving the air through but dirtying up the insides?

no, your cooling scheme is correct. Just dust the case out with a can of compressed air from time to time.

A bunch of exhaust fans cause negative case pressure and every small opening becomes a debris collector.

Positive case pressure, ideally with filtered intake(s), makes a remarkable difference in keeping your case clean. One or two big 120's running on 7v, pulling through filter media, keep a case quiet and clean.

Internal spot cooling like CPU, GPU, chipset are necessary in either arrangement but the clean case with equal air exchange makes them more effective without maintenance.

For floor-standing systems the difference is like night and day.

Well TBH I'd have the front run outtake and the rear run intake, esp. if the fronts are near the HDDs.

However you have it, filter your intakes if you are collecting dust.

Take some measurements. Pull the system out, clean it thoroughly, mark the date three months from now, and on that date pull it out again and check to see how dirty it is. If you are building up substantial dust inside the case after 3 months, you probably need better filters on your intake fans. Placing a system on top of a desk can also help lower dust levels. Dust tends to settle, so more is found near the floors, especially if your system is sitting on carpet. Carpet fiber floats when disturbed but quickly settles.
Most system designers place intake fans at the lowest point in the case and output fans near the top so that convection forces (hot air rises) work with the fans and not against.

It's been brought up in the above posts, but yes, there are fan filters you can buy. Look for them in the fan guard/cover section of the store. It attaches directly to the fan housing through the screw holes. Even better if you can get those silicone screw stumps that you can stick in to help reduce vibration.

The filters aren't much more than a mesh or cotton/steel wool type setup. It will grab the dust as it passes through.

Makes for bad airflow. The back is always exhaust, because the PSU fan is exhaust. If you have an intake and exhaust running next to each other you get turbulence, which keeps air in the case longer and raises temperatures.

*shrug*

That's why I prefer to duct the PSU fan somewhere else or even reverse the PSU fan. You're right, they should both be going in the same direction, but making a poor flow just because of stupid PSUs is silly :)

I prefer having fresh air over my CPU / video card then my hard drives.

My thought is that it's going to collect dust no matter what you do, so just clean it out every 4 or 5 months and dont worry about it :D