Well mine almost certainly won't be washed again this year, I've washed a car in sub-zero temperatures before, it hurt and the car was dirty again the next time I drove it.
I definitely wouldn't take it to a car wash or the Poles, they inflict too many scratches and do a lot more damage than the salt will if it's just left alone. The car is wearing a thick layer of Collinite for this reason.
Besides, this was her the other morning (street got a lot worse after this was taken) and I just don't have the heart to remove her icicles!
On the de-icing front, all you need is a 2 litre bottle of lukewarm (NOT hot!) water, chuck it all around the screen and side windows, hey presto, instantly de-iced glass AND wiper blades (de-icer actually makes them colder and stiffer AFAIK) which clean the glass quickly to prevent re-freezing.