The images show a debugging menu with the option to "show in compass," that is purportedly going to show up when the upgraded iPhone debuts.
One of the interesting things you can do with a digital compass is introduce augmented reality-type applications, as MacRumors suggests. Mobile augmented reality can use a phone's camera and compass to let a device capture an image of a location, like San Francisco's Union Square, for example. Information from the compass would allow names of locations to pop up on top of the image.
While this would be new for the iPhone and for Apple, others (like Nokia)for several years. has also looked at the usefulness of mobile augmented reality.
A digital compass also allows for the iPhone to catch up to the G1's capability of doing Google Maps in "compass mode." In the Street View mode, as you move the phone around, so does the view of the map.
We won't find out for sure until Apple does release the next iPhone, which is expected to happen sometime this summer.