The upcoming AMD 690G chipset (previously codenamed ATI RS690) has some tweaks to improve battery life on laptops.
Instead, the main point is that the K8, with its on-die north bridge, cannot go into a proper sleep mode when idle as a shared memory graphics controller needs to continuously access the memory. With the RS690T, this is no longer a problem as it can use the local store and let the CPU drop into the lower power state.
The next neat trick is something that this hack's Sony laptop half-heartedly implements. When you're doing 90% of your work, then the chances are you do not need lightning fast 3D performance, so integrated graphics is fine - especially if it can cope with Vista's Aero Glass malarkey, if that's your bag. And it will use a lot less power. However, try to play a reasonably modern game, then you're going to be watching a slideshow.
One of the other cool features of the AMD 690G chipset is the ability to hot-switch between the built-in X1250 GPU and an external graphics card. This gives you the ability to increase battery life in specific cases when you don't need the extra horsepower.