Alternate reality gaming (ARG) is a relatively new trend beginning to gain serious traction.  At its fundamental core, an ARG is simply a communication rich, collaboration environment that coalesces the real world and virtual space.  An alternate reality game bridges the metaphysical disconnects between the two environments.
 
I recently began using foursquare.  The folks over there tout foursquare as 50% friend-finder, 30% social cityguide, 20% nightlife game.  Foursquare provides a virtual world, that interfaces with the real world.  Registered users use Foursquare to connect with friends, update their location ("checking in"), describe what they are doing, and receive points for doing so.  The point system and earning badges (the gaming aspect), provide users incentive to do and try new things.  Additionally, it encourages them to share information.  "You should check out this bar and try their microbrew!"  Users themselves provide knowledge rich information specific to a target location.  The community makes the system more intelligent and capable of meeting profound knowledge management needs.
 
From a security perspective, the question I find myself asking, what utility can be found in this information?  Instead of focusing upon it at a micro-level (privacy, dangers of sharing location, social engineering, phishing, etc) it is far more interesting to look at it from a macro-level.
 
A paradigm shift in social media is coming in which the real world and virtual space interact together as a singular entity.  This entity is comprised of three fundamental components; people, location, and knowledge.  These three components lay the foundation for a dynamic, living, breathing system that evolves over time.  The system evolves around how these components are built and structured around each other.  It is somewhat analogous to an iterative mathematical process in which operators and operands are used to create complex equations and theorems over time.  These complex equations and theorems can then be used as the foundation for future equations and theorems...and so on, and so on.
 
What is most interesting are the relationships that form between people, location, and knowledge.  These relationships build around each other to create profoundly rich links and ties that essentially act as the system's DNA.
 
With all of this information, security folks could create models to uncover interesting relationships between individuals, location, and the knowledge associated with them.  One could then simulate potential outcomes by incorporating variables into the model.  This would enable security professionals to predict future relationships between individuals and their locations and thus reveal common threat indicators and patterns.  These models used for exploring existing relationships and simulating future relationships (based on variable inputs) would, with hope, provide cogent foresight for law enforcement.