Apple has been granted a patent by the USPTO for technology which lets it identify users based on how they hold their handheld device.
It uses sensors to identify the manner in which you hold your device and then use the information to load your user profile with customized settings and preferences.
Taking it a step further, this could also be used in applications which could create virtual button panels positioned according to how you are holding the device, allowing you to hold it anyway you want.
The basic patent claim is for
A handheld device, comprising: a sensor arrangement comprising a grid of capacitive sensing points configured to generate a pixilated image of a hand of a user in contact with the handheld device; and a controller configured to determine an identity of the user based on the pixilated image of the user’s hand generated by the sensor arrangement, and configure the handheld device in response to the identity determination according to user settings stored in a user profile associated with the determined identity.
Apple recently also filed for a patent which allows it to identify users using biometric information like their unique heartbeat pattern.