Which is more efficient... Leaving thermostat at 75 degrees all the time or using programmable thermostat and raising temp when not home then lowering it before coming home? Won't the a/c have to work harder to cool off warmer house?

The jury has been out on that for years. You do save money with a higher setting but that comes with a decrease in comfort from the lack of humidity control.

Unless I am going to be gone for the weekend I just let mine run because during real hot weather it can take quite a while for the A/C to pull down the temperature to normal range.