@Daniel B: RemoteDesktop terminates the current user session when it connects, so that is not going to help you much if you want to monitor someone else's session without them knowing.

The technology to accomplish this in a much more effective and automatic way than the way demonstrated with the Mac is not complex, it's just not commonly installed.

This will probably change pretty soon, for example what Lenovo is bundling with a lot of their new models:

http://static.tigerdirect.com/html/veriface.html

http://www.brightcove.tv/title.jsp?title=1445017879&channel=537061027