I opted for it last year on my L&K diesel. I am not sure if it has ever come on as it uses the same dash light as the traction control. However as I drive regularily along country roads lined by big trees I wouldn't want not to have it. I agree Insurnance companies should reduce premiums if you have to opt for it, better still I think it should be made compulsory on all new cars.

ESP saved me from an otherwise-sure crash that I described here. It rarely operates for me but I was certainly glad of it on that occasion.

On the topic of its use on ice, there's a length of road near my Dad's house that doesn't get gritted in the winter and has an unusually smooth surface. The first time I drove down it I thought it was just wet but it turned out to be black ice over its entire surface. Turning the steering wheel has no effect whatsoever but after half a second or so, you could feel the ESP pulling you in the direction you wanted to go. It was surprisingly effective.