[nkurz]

> Converting water to steam takes about (from the top of my head) 5x more energy than it takes to increase it by one degree.

I think this greatly underestimates the potential of evaporative cooling. The "specific heat of water" is 1 calorie/gram °C --- that is, one calorie can heat one gram of water by one degree Celsius if no phase change is involved. The "heat of vaporization of water" is more than 500 calorie/gram at 100°C. That is, the energy necessary to convert a given quantity of liquid water from just below boiling to steam is not 5x the energy necessary to raise that amount of water 1°C, but 500x! You are probably remembering that this is 5x the energy necessary to take liquid water all the way from 0°C (almost frozen) to 100°C (almost boiling).