Last year we did not EVER turn on the central air. Instead we purchased an energy efficient window unit for our "dog room", which is a really weird name for our TV room!
When we re-did the room two years ago, while my son was still at home, we gutted the room down to the studs. This gave us access to the walls, to re-wire and re-insulate - replacing walls half full of old blown in cellulose with nice thick batts of fiberglass AND a vapor barrier! Since we had all of the walls open we even insulated the interior walls simply for sound. It was after all a bedroom. When the kid moved out we turned the room into the TV room complete with a futon sofa. The dogs have made it their favorite room - thus "dog room".
Since it was all insulated we just turned on the cool and basically moved in all during the heat waves. We even slept in there on the futon!
Now we have had the furnace mostly off for about three weeks (switching in on for a short while to "take the chill off" only rarely. Instead we are still living in the dog room (which is also the warmest room now), with one little CF light bulb and the TV playing Netflix movies. I think we are officially old hermits!
I turned my furnace off about 3 weeks ago, well mostly because I ran out of oil. I have a small electric fireplace heater that does a good job of taking off the chill at night.
We're still lighting fires in the evening, but it is getting not too bad here, even though the weatherman was calling for snow again last night and we still have very little bits of ice in our yard. Soon though!