So even though when you lay it down on the 4 little feet it is designed to sit on there is no vents on the underside..
But since I run my unit on a carpeted floor I was still concerned over proper airflow and potential dust and fiber intake. Which would be real fucking bad.
So what I do is take the 4 riser feet from my Wii fit board, the things that look like grey pucks. Flip them down so the cup or hollowed out part is facing the floor, this puts the rubber grips facing up. Put the rubber feet of the Xbox onto the rubber grips of the pucks you faced up.
Congratulations, your console is cooler and you finally found a good use for that Wii fit board...lol