One of the reasons Windows 7 runs faster (faster start up, resume, shut down, less churn during user sessions) is due to the re-engineering of how Windows maintains and activates services running in the background. Microsoft's Channel 9 has an interesting video with a Windows kernel developer whose team designed a new trigger-based service controller that enables service developers to mark services as needing to run only when certain conditions are met. This means Windows 7 can more intelligently manage when to make resources avaiable for services that employ this trigger pattern for starting and stopping. Less code that runs at any given time means Windows 7 has more resources available for foreground processes that impact users interacting with the OS. The net effect of this for users is a snappier OS.