Delivery time is super important--50% of the time. Maybe less than 50%. I never pay for express shipping on personal orders. One or two days is never worth $3 cost to me. Let alone a $12-20 charge.

I suspect super fast delivery is only a differentiator when all else is equal. At $6+/gal diesel, I'll take the cheaper item delivered by bicycle in a week. (A bit of a joke, but you get the point.)