You know, I wish I had spoken up when we took the survey. My concern is that some people were worried about condensation. They chose to use rain covers and I think some sealed their equipment on return in large plastic baggies.... is it possible they forced moisture into the warming equipment by doing so?
For the record, I shot with a 1D3 totally exposed, along with the 580EX II in the rain for about 2 hours. I even took on and off several times a 1.4EX, shielding as much as possible the open camera when doing so with my body. I had no failures in the worst conditions we experienced. I merely wiped everything down with a towel afterwards, and left it out on my bunk. I also used a 40D, with either a 24-105 or 70-200 f/2.8 IS. I chose not to use the 40D in direct rain, but had it out while on Zodiac cruises....no problems there as well.
Lucky, I guess.
Last August, I had a brand new 1Ds3 in a very light rain with the same 70-200, or a 400DO lens. In 15 minutes, I had an "Error 99" that didn't go away until an overnight drying - then it was fine. I didn't have that camera on this trip, as I have traded it away...
These failures seem random.