I have only dived in Asia, and have not had any encounters with fogging yet. I've used the Canon A95, A620, A640, 350D in a variety of housings and have not missed a shot due to a fogged up port.
The water temperature ranges from 26-29 degrees celcius, and the air temp is anywhere from 28-34 degrees. The closest i've come to "blue-nuts" diving is probably in Bali which has 20 degree waters.
i notice that most of the newer cameras dont really have a problem with fogging, and the dessicant packs can be more trouble than its worth. i've seen a couple of housings flood because the pack was caught in the o-ring and stuff like that.
i usually advise DUP students not to use dessicant packs unless necessary, but leave the ultimate choice to them.
perhaps using the auto-power off feature on cameras will help reduce heat build-up. at the very least, turn off the LCD screen when not in use. it prolongs your battery life too. i did 15 dives on 1 set of AA batteries while in similans last year.
