Is it more cost effective to turn the AC temperature up or turn it off?

Question

We live in an area where 100 degree days are not uncommon in the summer. We have separate central air conditioning units for upstairs and downstairs. During the day, we are usually downstairs. Would it be more cost effective to turn the upstairs AC off during the day (the temp makes it to 90 according to the thermostat) or set the temp to 80 during the day? We usually go up about an hour before bedtime and turn the temp down to 72.

Answer 1

I always advise turning the setting up a bit rather than turning the unit off. You will be "completely" recooling the area if turned off. This can actually cost more than upping the temp 6 degrees. When the temps are changed frequently, your furniture is also adversly affected.

Answer 2

My understanding is it's more cost effective to leave it on at a constant temperature at all times than to turn it off when you leave the house/room and turn it back on again when you return.  The A/C has to work harder to cool the room down again once you've turned it off...