This video came out at MacWorld last week. It shows a multitouch frame over a large display interfacing with OS X. It works like the multitouch trackpad that new MacBooks. Take a look at how the
manipulations gestures work (when they work), particularly the image rotation around 0:22 - 0:27.
The demonstrator holds down one finger and drags around with a second finger, but the image rotated around it's own center. It didn't track the demonstrator's fingers at all. I am guessing the gesture engine recognizes the gesture and applies it to whatever is on the screen under one of the contacts (like the stationary finger.)
The MacBook trackpad probably works the same way, but the trackpad is not a display device, so it is not expected to have direct interaction. When you take the same feature and overlay it on the screen, it is not natural at all.
This use of gestures is really just a shortcut for certain tasks. The image rotation in the video is functionally equivalent to using a scroll wheel on a mouse to rotate the image. You really don't need multitouch to accomplish what is shown. Multitouch is not used to it's full potential in this case.