It is well known that Mac laptops running OS X have great battery life. But this article makes that benefit explicit and identifies the reason as the operating system:

The Unexpected: Battery Life in OS X vs. Windows Vista

The quick summary of the article is this: If you run OS X on a laptop, you get about twice the battery life compared to Vista. Identical laptop. Identical tasks. The only variable is the operating system, and that variable can double battery life.

This seems impossible. For example, in the “Heavy usage” test, the screen is on full time, the hard disk is running full time, and the processor is under load. Yet OS X runs an hour longer. Where is Vista consuming the extra energy?

[Note that it can go the other way as well. In this article, a user complains about Linux having half the life of Windows.]

The only possibility seems to be the processor. The amount of processor load can change the power consumption of a laptop dramatically (demonstration here, and see the demonstration of power consuption in the video on this post). OS X either uses far less computational power than Vista, or Apple is doing something to throttle the CPU and still get everything done.

It seems like it would be easy for Microsoft to figure out the secret and double battery life. That would be a huge benefit.