Effects on camera of extreme weather?

It doesn't seem very likely that I'll ever have to worry about extreme heat, but I was wondering if there are particular weather conditions that could harm my camera or at least affect it's performance?

I'm pretty sure my model isn't weather-sealed and I would not risk taking it out in the rain, but I started to wonder about other conditions, particularly freezing temperatures and (if I visit the butterfly house) humid conditions?

Not sure if I can be helpful, but I have found the Canons to be be very resilient with weather extremes.
The biggest problem I had in (just above) freezing temperatures was the lenses fogging up if the camera was not given enough time when taken outside. I got around this but wrapping the camera in a plastic bag before taking it outside and trying to give it enough time to reach the outside temperature before taking it out of the bag. This would probably be a good idea in a very humid place too, but I have used my 20D in butterfly houses with no problems without using a bag.
I have used the camera in the rain, sleet, snow, howling gales, sea spray, thunder storms, dust storms etc, with no issues (Not for the camera anyway!) (It's not something I would normally do, but sometimes you can't miss the chance to get a shot!)
Heat isn't a problem, we go over 45 degrees C regularly here at home and the camera still clicks away. Obviously leaving it in the sun in those conditions would not be a good idea! I find that dust is an issue, so I never change lenses until I am safely inside.

Same as Sam, when snowboarding last year, had minor fogging when I went outside, but that quickly cleared, and the next day I allowed the camera to get used to the temp, and had no fogging at all...

Very useful, thank you both

I'd been doing the wrong thing when out in the cold - having it tucked away to try and protect it

I guess that's one advantage of a secondhand older model though - I won't be quite as frightened to take risks with it as I would with a shiney new one