If you have a forced-air furnace, do NOT close heat registers in unused rooms.

“Your furnace is designed to heat a specific square footage of space and can't sense a register is closed - it will continue working at the same pace. In addition, the cold air from unheated rooms can escape into the rest of the house, reducing the effectiveness of all your insulating and weatherizing.”

http://www.powerhousetv.com/Energy-EfficientLiving/Energy-savingsTips/027471