What is the correct temperature for Air Conditioning?

One of the biggest points of disagreement about air conditioning is not whether to have it, but how to set it. Some Americans like it cold, and some like it hot, and the difference often plays out among gender lines, with men comfortable at cooler temperatures than women.
 
The debate is fiercest in office buildings where a single temperature is set for everyone, but it plays out in American homes, too. Around 20 % of American homes are set to 69 degrees Fahrenheit or lower when people are home in the summer. Another 18% are 77 degrees or warmer. There are partisans for 72 degrees, and 75 degrees, and everywhere else- a balancing act between comfort and cost.
There are difference from areas with high heating demand to ones with higher A/C demands. Air conditioning has become more common over that period, and homes have become bigger, requiring more energy to cool them.

All of that is counterbalanced by the fact that furnaces and air conditioners have become much more efficient over that time- especially air conditioners. The net effect is the US residential AC energy use is going up, but not by as much as heating energy is going down.
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Technology has the potential to continue improving the efficiency of both heating and cooling. Variable-speed air conditioners already on the market as a premium product, have the potential to reduce AC energy usage by 25-30%. On the heating side, one trend is towards heat pumps- essentially an air conditioner running in reverse. Because these run on electricity instead of fossil fuels, they can significantly reduce emissions in areas where a big portion of the power grid comes from clean sources.