I think it could actually be done. I know my MBPr has accelerometers in it that can be accessed.
(visit http://mrdoob.com/projects/chromeexperiments/google-gravity/ with Chrome on a MBPr)
(visit http://mrdoob.com/projects/chromeexperiments/google-gravity/ with Chrome on a MBPr)
The MacBooks with mechanical hard drives have the motion sensors.