The best a cooler of this ilk can do is to move some air around the notebook mounted on it. That may marginally help to cool the system as a result of more moving air around it.
You can get a similar effect, free, if you use the notebook on a hard surface, especially if you can raise it slightly off of the hard surface (say .5 inch or 1.5cm or so).
As pointed out, notebooks are not really designed to run at 100% all of the time (most games stress notebooks significantly). That being the case, they run hot. Also, using the notebook on a soft surface (like your thighs, on the couch, or carpet) limits airflow and makes the heat issue even worse.
The best use I have seen for one of these sorts of coolers was with a PS3 that was located in an enterainment cabinet of a former co-worker. His PS3 was running hot due to limited airflow. To keep his wife happy and to minimize impact to the aestetics of their living room, he set his PS3 on one of these type of coolers to increase the air circulation in the cabinet when the system was in use. In that case, it made a difference.