It seems like Nvidia is working on a new technology called Hybrid SLI and it will enable you to use a combination of integrated and discrete graphics. It will not only allow for increased performance during 3D, as it is also a power saving technology.
When the discrete GPU isn't needed, say for example when you're doing mundane Windows tasks, the discrete solution will be powered down and the integrated GPU will take over, thus reducing the power drawn by the system.
If this sounds familiar to you, then you'll be glad to know that AMD actually announced its PowerXPress technology a little while back for its next mobile platform. Nvidia isn't specifically talking about notebooks here though, as it works just as well on a desktop system.
It might not be that important to most of us, since even discrete graphics cards draws a lot less power in Windows than they do during 3D work, but with power saving in general is becoming more and more of an issue, those few Watts saved might have an overall impact on your power costs.
It's not clear when this technology will be available, but it should launch alongside the upcoming MCP78 and MCP79 parts with integrated DX10 graphics. We'll bring you more on the subject as we find out more specific information.