One of more interesting features of the latest round of portable Macs is something called the SMS, or Sudden Motion Sensor. In addition to being able to detect acceleration, the SMS can also provide the Macs orientation in 3D space. If you were thinking that this ability would be a great way to detect if someone is messing with your Mac, then you'd be right.
Check It Out: Worried About Your Mac Getting Jacked? Get JackSMS