ATI and Nvidia have discrete chips and driver capability that can switch the discrete chip off and turn the IGP on. This is a feature that will be supported by Arrandale 32nm notebook CPU that features 45nm graphics in an MCP packaging.
The Arrandale graphics will be able to work with spreadsheets and some basic operations such as Windows Aero, while the discrete chip could take over if you would need more power for your CPU.
Naturally the Clarksfield quad-core notebook CPU, scheduled to launch in Q3 2009, won't support this feature as neither CPU or Mobile series 5 chipset don't have an integrated graphics card.
The good news is that you will be able to turn Intel’s integrated graphics off, and this will certainly make many people very happy.