Essentially, a CAI is a supporting mod for making more HP with other mods like nitrous, cam, ported heads etc... If you datalog your vehicle and it shows 99+ KPA at WOT throughout your rev range, you're probably not going to see a gain from CAI. You can see a gain from a CAI if that number dropped below 99, which would indicate a restriction in the air path.
One of the things NOT mentioned in that article is the fact that some CAI's can take advantage of bringing in cooler outside air (opposed to hot under hood air). Cooler air is denser air, and that denser air will make more power at any given rpm. This is the reason your car/truck feels peppier on cold days. Also, because dyno rooms are typically hot, this may not even show up as a gain on the dyno. It could, however, be felt on the open road and may even show a gain at a racetrack. It's the same principle as a true cowl induction hood back in the 1960's.
Mike