I have a single room unit in most rooms of the house. I know central air would probably be more cost effective. When we did have central air, I'd turn it up to 72 and still had a room unit in the bedroom set at 64. I don't deal with heat well. The extra money we spend in the summer to cool, we save in the winter for heat. I program the heat to kick on in the morning to 68 about an hour before the kids get up from school, then it goes back down to 65 for the rest of the day.

I keep a fan in my window all winter long to keep it as cold in here as possible.