According to Wikipedia "heat build-up in notebooks is reduced by 15 to 20 percent, when a laptop is situated at an angle compared to a laptop in a horizontal position". http://en.wikipedia.org/wiki/Laptop_cooler
I use an external monitor and keyboard, so it doesn't matter if the laptop is in a horizontal position and it seems a very simple way to improve cooling. My only concern is the hard drive, but probably it doesn't care if it's not completely horizontal.
Have you tried improved cooling with this technique? Did it help?