I have implemented many of the same solutions as the others have posted, fans and lights turning themselves off. Here is something I did not see yet.
I installed a water recirculator to get hot water to my kitchen. It is really nice not having to run the water for 3 minutes every time I want hot water. The pump shuts itself off when the hot water gets to the sink, which is supposed to save me money. With the ISY I made this even better. I only allow the pump to run when a light is on in the kitchen or the master bathroom. When we get up in the morning by the time we get to the kitchen the water is already warm at the sink. At night when we come home and turn on the kitchen lights the water warms right up.
For me, the most important thing is that the pump does not run at all when we are out late or go on vacation. The ISY "Knows" when we are sleeping, and it knows when we're away.
The same functionality is going to be implemented with my bathroom underfloor heating and A/C. As soon as Michel releases the DSC (alarm system) to ISY link my ISY will know when we are away from home. It will automatically know to keep things turned off.
My ISY-26 uses so little energy. I'm sure I'm easily saving more then it uses. Which is a plus, as I would use it even if it did not save me energy.
Scott