If you have a good branded laptop, its thermal properties &
heat dissipation ability should mean you dun need a separate
cooling pad. That shld be ur key starting point.
I really think its a gimmick. If your laptop hangs due to
overheating thereby necessitating one (I've seen a friend's
case)... u've gotten a bad brand of notebook or a lemon specimen. U
shld get warranty support.
Drawing additional power just to cool the base is not sensible,
practical nor environmentally friendly. Even a USB bus
powered one draws 5V up to 500mA.