A post over at gizmodo links to a concept for a one button off switch for your house to turn off all non essential items when you leave the house. http://gizmodo.com/gadgets/tree-huggin/house+off-button-makes-going-green-easy-264876.php
It's just a concept but a good one. Though really it's been around for a long time. I've seen quite a few hotels in Europe and China that have this built in to the hotel rooms. When you enter, you put your key in a slot right next to the door which turns power on to most of the outlets in the room. Something like this
This sort of system should turn off the a/c automatically when you leave too. Normal thermostats can be set to do this based on a schedule but for people with variable leaving time you have to set it to your latest leaving time which isn't ideal. (a 7 day thermostat approximates this)
Also, by turning things off at the outlet you eliminate all the "zombie" power suckers, like wall warts and electronics in standby mode that you can't turn off without unplugging.
Basically it all comes down to making it convenient to turn things off.