Like Craig, ignoring the hysteria about thermally shocking a windscreen was the best winter driving tip I ever learned. Not having to wait for the cabin heater to defrost the windsreen is real boon.

Sticking with the ~25/75 glycol/water ratio as an experiment. Last winter I flipped the ratios around hoping the engine would run a little warmer. Tempted to drop a litre out of the sump if I can muster up any enthusiasm to crawl underneath the car.

I'm not sure if it applies to warm water (as opposed to boiling water), but it may make your windscreen deteriorate and be more susceptable to cracking.

I've done it for 20+ years on all sorts of old snotters, from my B GT to Fiestas, Escorts etc right through to my current company car. Even my previous Mondeo with multiple repaired stone chips ... no problems with cracking etc.

As long as the water is only hand-hot, it's fine.

More cars should have Ford's heated windscreen though, it is a genuine safety aid (admittedly I found it better at demisting the inside of the screen than for clearing frost)

I use a large kitchen jug to lob warm water (not hot) onto my windows, scrape them down with an ice-scraper and then get in and put my heater on full fan. Having a little car means that the cabin heats up very quickly, and the fabric roof is actually very well insulated. I think most people have those heated rear windows and if I switch mine on, the wing mirrors heat as well. De-icer is horrible stuff.

Normally use the container full of warm water very successfully. However in these colder conditions, -4C and lower, finding that the water re freezes after using the wipers.

Then sprayed on de-icer which visibly melted the ice but when it ruffled up in the 30mph airstream and I used the wipers, froze again. A bit stop start until some heat got through the vents.