Sometimes a piece of wood/paper
or a book isn't enough to cool down a laptop when you're working for more than a few hours; laptops like the MacBook can get awfully hot after more than a couple of hours, and it's not just your thighs that are in danger of getting burned...the components within could are endangered with failure as heat is a computer's #1 enemy. Or Windows Vista...I jest, I jest [ducking] (Go Windows 7!). For those looking for something a bit more serious in regards to laptop cooling on the go, the Belkin Laptop Cooling Stand is a more than viable options thanks to a couple features...
The Belkin Laptop Cooling Stand is designed to push airflow upward onto the laptop surface, following the natural direction of rising heat; a "wave" design provides space inbetween the cooling pad and laptop surface where a single USB powered fan pushes cool air up onto the laptop, and then channeled out the sides. Wonder if this airflow is noticeable for the user, something pleasant in winter and not so welcome in hot summer months. Available in white or black for about $21 on Amazon
Options for affordable and DIY laptop stands: