What appears to be an Intel video posted on YouTube suggests that an accelerometer in an Ultrabook can make your interaction with the notebook much more interesting (and probably not just for the user). In a very simple application you could, for example, control a tennis racket by moving your notebook through the air accordingly, and swing the racket at the ball.
From a software engineer's perspective, this may be an interesting idea. But, as a user, do I think that my notebook, even if it is light, resembles the look and feel of a tennis racket? Nope. And let's not imagine a javelin competition, even if there are computers you would want to throw out of the window occasionally.
According to the engineer's presentation, moving an Ultrabook instead of using keys is how "kids and children could experience the Ultrabook in a different and a beautiful and reimagined way." I am not sure how many kids have been consulted when Intel came up with this tennis racket demonstration, but speaking from experience, kids occasionally lose control over Wii Remotes. The last thing I would want to see flying through my family room is a $1000 Ultrabook.
The video was not posted to Intel's official YouTube channel, so it may not have full corporate approval, especially with the title "Bounce a ball with your device." Unless this software comes with some sort of insurance and a free product replacement warranty, there may not be much opportunity in the real world. We still live in a world in which a notebook should remain in a stable position on a reasonable horizontal surface. I don't see many people bouncing balls with their Ultrabooks anytime soon.