Martin, your dad doesn't have it on his X5...?

Nope... at least i'm 95% sure that no.

I learnt to drive on dad's E60 with active steering, and mum's Golf has a similar variable ratio system which I drive now and then.

I wholeheartedly agree that on a smaller car it is unnecessary and kills steering feel; it's unnaturally light and in my mind takes away from the driving experience. Dad enjoys it on the E60 because of the ease of parking and low-speed manoeuvrability but I never enjoyed it for the reasons outlined above.

But for the bigger X6 I'd defintely say go for it as lugging a two-tonne X6 around without it in inner city driving wouldn't be too fun.