Best way to quickly defrost car windshield?

I read on ehow.com that one way to quickly defrost your car windshield is to pour some rubbing alcohol into a spray bottle and then to spray your windshield with it. The alcohol is supposed to quickly melt its way through the frost and loosen the ice from the windshield. Has anyone done this before and did it work well? I don't want to spend 10 minutes sitting in my car with the defroster turned on (is it bad on the engine to leave it idling for so long?) nor do I want to stand out in the cold and use an ice scr. I've also heard that it's bad to pour hot water on the windshield due to the possibility of the windshield cracking. If anyone has used a de-icer spray before, what is a good brand that works well? Thanks!