[rkagerer]

Another tip: Blowing air onto a component, instead of sucking it away, is much more effective for cooling. Basically if you put your hand where the cooled component is you should be able to feel the airflow.

In practice this meant flipping the "exhaust" fans in one of my systems. It resulted in temperatures that were consistently a few degrees lower. Note in this instance there wasn't any ducting involved.

[tadfisher]

Yes, positive pressure is also essential for keeping dust off components, which becomes insulating if left unchecked. Make sure intake fans have filters and you're golden.