Integrated Graphics

Good evening,

I'm building a new PC at the moment, and the whole time I was wondering what happens with the integrated graphics chip when I use a dedicated graphics card. I mean, is all that power just lost? I've read about "Lucid Virtu MVP", but that's not quite was I was thinking of. (It also doesn't seem to be quite there yet, but that's another story.) Couldn't my integrated chip just do all the windows work for me, including YouTube and all that stuff? This way, while being in Windows, my dedicated graphics card could basically do nothing, which I imagine to be quite nice in terms of power usage. Also, when I run a game (or any other high-performance-3D-app) in windowed mode, the integrated graphics card could render all the windows stuff, and the dedicated one could concentrate on the application itself. Also, does the integrated graphics card get used with video rendering or similar applications automatically? This concept seems so obvious to me, that I can't resist asking if any (consumer) motherboard/setup does support this, even though I can't really find anything on that matter.