I agree with the above posts as well. Although living in Toronto we do not have too many real cold nights, but when we do, the windshield frosts over very quickly and when it does, it takes a really long time to defrost.
Personally I don't idle my Ford, simply because the temps don't go that low in southern Ontario and because it doesn't have a remote starter.
My wife's Mazda does have a remote starter and she uses it every morning. It has a 10 minute running time, but she hardly ever leaves the car idling that long. Even if she did, I’d rather have her and our children comfortable, than try to protect the machine that is supposed to serve us.
Besides, like I say in many "cold start" related threads, the engines don't seem to care, from a wear point of view, if the oil is thicker or thinner at startup, as long as it is pumpable.