I disagree with Ironlight, and with the article.
First of all: Negative pressure is a bad idea for both computers, and for media rack systems. The reason is, negative pressure means the computer case, or rack system will attempt to draw air into it through any crack that will allow air through it. This means you have no control over dust entering the case or rack. Unless you are constantly swapping equipment in and out of the rack, or components in and out of the computer, you will spend an excessive amount of time chasing all of the dust out. A computer case or media rack should ALWAYS run positive pressure (More intake pressure than exhaust) so that you can put filters on the intake, and capture all of the dust entering the enclosure. This will prevent a LOT more thermal failures down the line due to dust insulating the components, and clogging up fan bearings causing them to fail. It would take a VERY poor design to cause a thermal failure in a rack that had any sort of ventilation, as long as all the components are kept free of dust.
Second: Don't confuse computer cooling for media rack cooling. The two are very different animals. Computers have gotten to a point where they stick a lot more strictly to standards, which allow for simpler and cheaper solutions in a rack environment. For the most part, any rack-based computer system is built to draw cold air in from the front, and exhaust out the rear. Media systems do not stick so strictly to standards, so from one component to the next, you can not be assured where it will draw in cold air, or where it will exhaust hot air. The good news, is that media systems are typically not as sensitive to heat as computers. As long as you give them some sort of ventilation, not just locking them in a hot box, they will manage on their own.
As far as hot spots are concerned; the goal is not to avoid having ANY hot spots in a computer case or rack. The goal is keeping the hot spots from collecting around sensitive components. The way you do this, is by exhausting from as close to the component as possible. If the top of your rack has no equipment in it, who cares if there is a pocket of hot air sticking around up there ? If the 5-1/4" drive bays have no components in them,who cares if there is a pocket of hot air swirling in there ? As long as your active components are kept cool, the pockets don't matter. Once you find a component that generates a lot of heat, find a way to exhaust that hot air directly outside of the case or rack. As long as you are bringing cold air into the rack, that exhaust will draw that cold air right to your component. That is all there is to it.
I would never run a rack that had ONLY intake OR exhaust fans. There always needs to be something to guide the airflow. So either you seal the rack to be air-tight other than your intake and exhaust fans, or you run positive pressure with at least one decent exhaust fan to get the airflow moving in the right direction. The most efficient systems will always draw just slightly more air into the case or rack, than it expels through the exhaust. When you have a component that generates a lot of heat, make sure your design keeps it's hot air from blowing by the cold air intake of another component. The easiest way is by ducting from that spot, directly to the exhaust fans.
Ultimately, the biggest thing that will cause thermal failure in a media rack is dust buildup. The second is just letting one component cook the next component. If you manage those two things well, the ventilation part becomes much less important.