Now how many times has that idea crossed someones mind, let alone, how many people actually pour hot water on their windshield? DO NOT POUR HOT WATER ON YOUR ICY WINDSHIELD. It will only lead to cracking.
If you are in a hurry, use an ice scraper while your car is running the defroster. If you do not have an ice scraper, use a credit card to clean of the frost off of your windshield. IF you have the time, let the defroster do its job.
A way to prevent an icy windshield is to place a towel on your windshield the night before. This way the frost will settle on the towel, not on your windshield. Just remove the towel and off you go!