I also was concerned with the extreme heat from my appletv. I had it sitting on top of my cable box (which might have caused many of them to go bad). I just got done solidering together a usb fan to put underneth and cool it.
Basically i found the top to an old PSU that had an 80mm fan hole cut out. I took an 80mm fan and a usb cable. I used a 4 pin adapter for 3 reasons, It came with the fan, if i messed up i could throw it away, two lines are easier than three.
In the usb cable you will find a white, green, red, and black lines (i also found a copper wire). Solider the red lines together and the black lines together.
Peel the rubber off the bottom of the appletv, but be very careful because the rubber tears easily. use a paint scrapper or something like that to scrap off the glue on the bottom/ or use a toothpick to poke through the holes.
The nice thing about the old PSU top i found is that it lifts the appletv like 3 inches off my surface.
I can tell by feeling the appletv that this cooled it by atleast 5-10%. If I had more guts i would cut a hole in the metal, but so far i dont think i've voided the warranty
If you would like to see pictures or talk to me about it email me at
rosssgunderson@mac.com