Kinect, though, would be a nice cheap addition for digital signage in public spaces, illustrated by this hack and this. Some ad shops are already experimenting. Wouldn't be fun to customize a billboard's message based on the onlooker's body type and gender?
One other thing Kinect would be awesome for is monitoring people's general usage of TV and other media in the device's vicinity by combining sound detection and recognition with body position identification, answering the "what's on?" and "is anyone watching it?" questions. It's such an awesome idea that I'm actually keeping my Kinect behind the TV and facing the wall when it's not in use, in case the idea has already occurred to someone else.
Looks like Microsoft has tested a Nuads-like execution with Chevy Volt last fall with the car placed into the Kinect-enabled Joy Ride.
SoftKinetic has developed and been using its own hardware to power up signage way before Kinect.
Image by: AV-1