I was fiddling with work's Canon Rebel XTi camera, and noticed that when I hold it up to my face, the display showing current settings blanks automatically. At first I thought it was an automatic timeout, then I pulled the camera away from my face and the display turned on again! Once again, held it up to my face, display turned off.

Whoah! I found there's a little sensor that detects the presence of your face, and turns off the display when you hold it up to your face to take a photo. The sensor is just over the display and is probably capacitative, like the trackpad on most modern laptops.

I love well-thought-out interface design like this. It solves what would otherwise be a problem (glaring display just under your eyes when shooting) in a completely non-intrusive manner.

I even posted a video of this, because it's so neat.