Not only is this a concern on the desktop, where that monthly power bill doesn't seem to be getting any smaller, but the notebook as well. Battery life and heat are critical areas that currently can only be solved by reducing the amount of power used. Nvidia is playing on a technology we have seeing in the past, coupling both a discrete GPU and an integrated GPU. This “hybrid” SLI configuration sounds like it will be very automated, enabling a notebook to quickly toggle between using a discrete GPU when high performance is desired and an integrated unit when there isn't much demand.
Truly, this is something that anyone wanting a fast notebook could benefit from. More than that, however, it brings to mind a very interesting point: It could easily fit on the desktop too. When idling, an 8800 GTS in a desktop is going to be consuming more power than an Intel IGP at full load. Given the amount of attention given to energy recently, which will only grow, it makes sense to have similar technologies be given to the desktop: An on-board GPU for when you are web browsing, writing emails, et cetera – and a beefy GPU for when you fire up a game.
AMD saw some benefit in this when they brought Cool N Quiet over to the desktop. Many systems with it enabled will not even run their CPU fan due to the low power draw and heat output of the CPU when there isn't demand on it. What I would like to see is not only Nvidia, but every vendor from Intel to AMD to ASUS, invest in hybrid technologies like this.
As far as Nvidia goes, their new Hybrid SLI technology is supposed to be featured in notebooks before the end of this year, but few details were released. I look forward to seeing how they expand upon this.