The Dual Storm fan's purpose is much like the TMD fan, albeit with different construction. Rather than using a single fan with motors at the corners, the Dual Storm utilizes two fans that spin in opposite directions to create extra air pressure and focus airflow towards the center. With the added option of a fan controller, the Dual Storm should definitely help keep CPU temperatures down to a minimum.

http://www.insanetek.com/index.php?page=cmdualstorm