I'm surprised it doesn't freeze / frost up your windows, and make things worse than they were originally.

The biggie, though, is that this is potentially dangerous, though--the large temperature difference between the cold windshield and the warm water (30 F vs 120 F) may cause the glass to crack. This is why you're not supposed to put hot water in a cold glass, or vice versa.

In the winter, either wait for the defrosters to work, or scrape. And don't just scrape the front windshield--you should be able to see out the back and sides, in addition to having clear mirrors. (I grew up in Buffalo, this was a pet peeve of mine.)

A safer method is to put a small tarp, or even a piece of cardboard, over your windshield when you park the car for the night. Frost forms because the windshield radiates heat to the night sky and becomes colder than the air around it. Anything that blocks it from a direct "view" of the sky will keep it frost-free.

Yes, take warning that it could damage the window. I did that once, years ago, when I was in a rush. I thought I was a genius! But a small crack that was already in my windshield turned into a big crack in .15 seconds. Lesson learned.

Alternative: You can spray a vinegar mix on the glass each night to halt/hinder the ice from forming:

http://tlc.discovery.com/videos/street-customs-tech-tips-vinegar-on-windshields.html

Seems to me that acquiring and transporting hot water would be as much hassle as scraping, even if you've been reduced to using a credit card.

I've been doing that for years. I use room temp water though. I just fill up a large drinking water bottle and take it with me in the morning. Never had a problem.

We once totally cracked up our hot windshield at a gas station in California in the opposite fashion, foolishing pouring a cooler of ice-cold water on it. Dumb dumb dumb.

There has been a great product available for years in a pressurized can that features an ice scrapper and saw tooth claw for scraping through a sheet of ice.

I want to say that the can is silver with a red plastic dispenser/claw/scrapper on it, but I can't recall the name... and I KNOW i've seen a yellow top can labled with "Prestone" recently.

It's definitely worth shopping for. We always keep at least a can in our cars and one in the house, just incase the doors are frozen and we can't get into the car to get to the can of de-icer.

PS: I've heard of people installing remote starting to heat up their car before then come out, but I keep hearing about car fires, and I wonder if they are related?

Hot water - no. Warm or room temp? Sure. I've also found the windshield fluid from the wipers works pretty well for a light frosting.

That's how I always do it. Have been doing it for a decade, and I've never cracked my windows. Not super hot, though, just warm.