The patent allows for building monitoring sensors into a case, screen or even earbuds. Depending upon the method used, when someone holds the device or swipes a finger across the screen to unlock, embedded leads will read the EKG information and allow the device to perform actions based upon result. A built in EKG has far-reaching medical potential, but the patent deals mostly with issues of authentication. Different profiles can be saved on the device, similar to having multiple user accounts on a computer. This would allow multiple people with different profiles to be accurately authenticated and provide differing device capabilities. Uses can include anything from preventing children from using certain apps, to allowing the proper user access to online banking and other financial transactions. It can also be used to save different user information that's embedded in apps allowing a great deal of personalization such as one device keeping individual Dropbox information, allowing the proper Dropbox to be accessed by the person holding the device.
Integrating this with an earlier Apple patent can allow the device to read and react to your mood. This sounds kind of out there, but it can be used for all sorts of neat things. If it reads you as being angry, potential calming songs in your iTunes library, or relaxation apps can be suggested. I can see a nice tie-in with iAds.
I wouldn't get too excited about this, at least not presently, since Apple patents an awful lot of stuff that never sees the light of day. But if they can pull this off, the possibilities seem endless.