Here's some speculation that definitely came from the House of Crackpot Theories, but since it's kind of a slow day with the holiday today, feel free to let your imagination run wild. This video suggests that the next iPod touch could use its internal gyroscope and the FaceTime camera for a sort of pseudo glasses-free 3D. Icons on the home screen could tilt and shift according to how you're looking at the phone, and games could bend and shift around as you move the phone and your own head in the camera.
It's highly unlikely that we'll ever see this in the official iOS, however. Nintendo is set to release its glasses-free 3DS system in Japan this week, but Apple has never really shown an interest in the technology, outside of various random patents and some compatibility features for OS X.
Still, it's definitely possible to create this kind of visual with an iOS device, and while I've never seen an app use the FaceTime camera for head-tracking, it certainly seems like it wouldn't be a tough thing for a talented developer to do. Maybe as the 3DS gains some popularity, we'll see some developers try more of this on Apple's iOS platform.