The Kinect for Windows development team in Redmond have just posted an excellent article on Face Tracking, along with a bunch of code samples for managed code developers.
MSDN has had an article on Face Tracking for a while now. The code is all native C++, which possibly makes it appear a bit harder than many developers would like.
Providing another managed code introduction can only be a good thing to help .NET developers get started with building a face tracking application with Kinect for Windows.
Just to be clear this is about face tracking and not face recognition.
Face tracking will enable an application to identify the direction a head is facing and match some facial expressions, such as happy (turned up mouth) or sad (lips turned downwards).
Read the article here
Mysteries of Kinect for Windows Face Tracking output explained