I just had my hard drive replaced by Weaknees (a terrific experience, by the way) because the original one died. Since I keep all my components in a cabinet, I always suspected it might get a little too hot in there. While my unit was back getting repaired, I picked up an inexpensive "notebook cooler." from BJ's Wholesale Club for about $25. This is what it looks like: http://www.antec.com/us/productDetails.php?ProdID=75004.

It's perfect because it plugs right into one of the USB ports in the back of my Tivo unit, runs on about 2.5 watts of power, and is very quiet. It's about 1" high, so the Tivo unit sits easily on top of it.

So far, so good.