A dimmable CFL would save on the order of 60% vs. 15% for this incandescent dimmer. The higher bulb cost is at least partially offset by the fact that this dimmer is fairly expensive.
Also, it seems you can duplicate the energy saving technology in the dimmer by manually reducing a regular dimmer a tiny bit from maximum.
i gotta say, this is a fantastic idea, which is why i spec'd it in my most recent project (my own house). that being said, it sucks to use. the buttons feel flimsy and almost everyone that visits is confused by how to use it. they all end up using the dimmer to try to turn lights off - which actually just leaves them on all the time, thereby probably making them less eco-friendly than a regular system. i would not use this system again and would not recommend it until they make improvements.
Consider LED Lighting Solutions, they are the real future to lighting and saving energy.