Microsoft, the company geeks love to hate, is going to make itself eligible for the award of greenest company on Earth. It would be churlish to ask why they haven't done this before - energy inefficiency is mainly a product of computer manufacturers rather than Microsoft.
It's an interesting idea that it's possible to save that much energy without putting too much effort in. 100 million computers seems to be quite a low estimate for the number of computers in the world - I seem to remember seeing a stat that there were almost a billion computers in the world.
Anyway - we'll see if this actually adds something to the computer or if it just makes the computer constantly try to turn itself off when you're not looking.