While EPA power savings are far from novel. AMD has managed to integrate much of the mobile technology into desktop graphics cards. The benefits will results in meaningful savings over time. AMD ZeroCore does better than the PowerTune seem with the last generation cards like the Sapphire HD6970.
Starting with the Southern Islands GPUs such as our Asus HD7870-DC2-2GD5-V2, AMD is introducing ZeroCore Power, their long idle power saving technology. By implementing power islands on their GPUs AMD can now outright shut off most of the functional units of a GPU when the GPU is going unused, leaving only the PCIe bus interface and a couple other components active. By doing this AMD is able to reduce their power consumption from 15W at idle to under 3W in long idle, a power level low enough that in a desktop the power consumption of the video card becomes trivial.
Long idle is when the screen is powered down. Even older CPUs like our Phenom II X4 965 Black Edition can idle at 1W. Motherboards have also improved considerably with chipsets able to reduce PCI Express power etc.. While Windows 8 and above do use the GPU, closing any browsers etc will allow the machine to enter the lowest power states.
AMD ZeroCore also benefits CrossFireX setups by shutting down secondary cards when not needed. On the multi-GPU Tahiti card, the slave GPU can be put in an idle state, leaving only the master GPU and the PCIe bridge active. Coupled with ZCP on the master GPU when in long idle and even a beastly multi-GPU card should be able to reduce its long idle power consumption to under 10W after accounting for the PCIe bridge.