I associate business trips and hotel rooms with long showers. When you grow up with a lot of siblings or in an apartment building with apartment-sized water heaters, you learn to take nothing but short showers, because there's always someone outside going "You better save me some hot water."
Even in a hotel, though, I feel guilty about letting the water run for too long; endless hot water aside, it's wasteful. So I'm hoping the Ecovea shower system by Reveeco sees some uptake. Promising a savings of up to 80% on both water and energy, the Ecovea system recycles water for immediate reuse, letting you shower in a sort of guilt-free loop of the same water.
I know that sounds potentially gross, but the manufacturer claims that the recycled water is "sometimes even cleaner than the source water from the supply system."