Most if not all the attention surrounding Windows Vista Service Pack 1 has been around performance, reliability and compatibility, but you probably didn't know SP1 also makes short strides in terms of Vista's power efficiency. And by short, I really do mean short because we're talking about improvements in the magnitude of only a couple percents. That in the context of 5 hours battery life is a mere additional 6 minutes. Having said that, some is better than none.
The first of two improvements is in the display subsystem. Starting from SP1, the VSync in the Desktop Window Manager (DWM), intended to give a glitch free experience, no longer runs continuously. Instead, the interrupts are disabled after a short timeout period where no screen updates has occurred. The catch is that a screen update can be anything from a blinking cursor to a flashing network icon, so the chances of a screen idle might be a lot less than you would imagine. The second improvement is in the audio subsystem and only concerns those with HD Audio codecs. Whereas in the RTM, the sound card would never idle even if there was no activity, in SP1, the default idle timeout for has been changed to 30 seconds; after the time, the OS will switch the audio device to a D3 power state, meaning the device should not consume any energy at all.