we keep the basement (playroom) at 65, and the rest of the house at 60. All day and night. We use our fireplace to keep the middle floor warm when its really cold out and love to sleep in chilly beds (great snuggle time!)
If my kids get cold, which is rarely, we put more clothes on, or blankets.
Oh, and some people think having the fireplace can suck the heat out of the room, but we found
this that totally cooks the whole middle floor and then some!
Sorry for the shameless plug here but this thing rocks!