I recommend reading the article in the February issue of WIRED Magazine about 10 mobile applications that make use of GPS to offer smart and/or entertaining services. (The article is available online as well. )
This will give you a glimpse of what is on the horizon with GPS-enabled mobile applications as devices gaining more and more adoption by consumers.
The list of 10 is fairly US/Western world centric so I would not be surprised to learn more about applications that support some fairly exotic use cases. If you have interesting examples from the Middle East, Africa or Asia, please post them to the comments!