In my case, ventilation was definitely not what caused the reformat. I have one of those Thermotake USB fans pulling air out the right side of my HWS. I have used the diagnostic menu on the HWS to look at the hard drive temperatures, and they were very low (high: 114F, low: 97F, average: 107F). That is well within spec.
I was out of the house when the initial problem occurred. When I came home, I noticed that our digital clocks were flashing, indicating that the AC power had gone out (there were flash thunderstorms in the area). I am wondering if that is what might have caused the problem.The Olympics might have been recording at the time of the power outage (not sure).
Anyway, the HWS hard drive has been working normally since the reformat. I sure hope that I do not get another reformat. I lost over 140 recordings this time! Luckily, I have been able to find episodes of the shows that I really wanted to watch on the internet. As I said, this has happened to me before, so usually, I transfer shows that I do not want to lose to my EHD, but I guess I got a little lazy this time.
EDIT: Corrected the values for low and average temperatures.