How does the 'hardware microphone disconnect' on clid close work?

I haven’t put my hands on the new Air but I doubt it will work much differently than other Macs. Lid closing causes a sensor in topcase being activated by a magnet in the lid, a pretty simple and efficient mechanism. When sensor is activated the system is instructed to change power state and go into sleep mode and in most modern machines, if I remember correctly, after 3 hours into hibernation mode. The change of power state implies that a set of power lines (all S0 lines used by the Pc up and running) are switched off and get no power from the system until the lid changes sensor state again. Hope this is the info you were looking for..