According to details leaked from the Build 7850 M1, "Detect Human Presence" is one of the features which the Windows 8 operating system will sport.
"Detect Human Presence" is listed in line with additional features such as the accelerometer, ambient light, detect your current location, orient your display automatically, proximity, etc. One interesting mention reveals that "Sensors can detect information about your computer's location, surroundings, and more."
While it's clear that the accelerometer can be put to very good use on next generation form factors such as slates /Tablet PCs, it's a bit harder to guess what scenarios would involve a feature like "Detect Human Presence."It could be used for a Windows 8 version of Kinect.