I don't think the liquid de-icers work that well. I used to use the concentrated stuff in the spray cans and I would be leaning out the window spraying it directly onto the windshield in a blizzard coming over a mountain pass, with visibility reduced to a little peep hole and the wipers frozen into chunks of ice, the defroster roaring full blast and the wife yelling at me to close the window. Now I have an electric in-line wiper fluid heater and electrically heated wiper blades, which gives much better results.
I found the Safe Vu here:
http://www.myles-rec.com/Transportat...uid_heater.htm
The one I have is described here:
http://www.microheat.com/hotshot/why.asp#
I think there are also washer fluid tank heaters (both electric and using a heat exchanger with engine coolant), but they take awhile to warm up. I think some Mercedes come stock with windshield washer fluid tank heater. Also, Range Rover has electrically heated windshield as OEM, but I would think that would make windshield replacement a bit expensive.