Imagine you own a small retail shop of 1-2000 sq ft. Too big for a stop 'n rob mirror and way to big for 1-2 on duty employees to keep track of 5+ customers. So you go the standard route of 5-6 security cameras.
Now, during a morning physical inventory you dicover that 1 itemX is missing! Now what's the point of having all those cameras if you're not going to use them to catch a theif? So you start from the last inventory (ideally 24 hours ago but I've known retailers to only inventory on a weekly basis) and you sit and fastforeward through 8-12 hours of tape to try and find out where itemX walked off. If/when you find him you may not have his face... so you pop in the tape for the front door camera start at the time he took the item and rewind back until you see him walk in.
In short, getting your video evidence can take up to four hours of a small business owner's valuable time!
Now imagine a security system that stores an image of every face that comes through your door, tracks the location of every customer in the store, and can tell you who went by a particular location and WHEN. Now when you dicover itemX has walked off you go to the security system, indicate that 1 itemX was stolen within the last 24 hours, and within seconds you have a picture of everyone who walked by itemX and can zip directly to the video of everthing they did while next to itemX.
The technology exists to do this and the most expensive part is the software. Are there any reasons why such a system isn't commonplace? I mean, if this could be profitable, I'm all over it.

Also, since many shops already keep a customer database that tracks purchase history... why not link the above system into the customer database. So when customer #23497 walks in the door the employee gets a little box on the register that says something like:
Mr. Smith just walked in.
Recent Purchases:
itemX - 4
itemY - 1
itemZ - 12
Items on order for Mr. Smith:
item42 - 1 BO (Back Order)
item0 - 2 OH, 1 BO (On Hand, Back Order)
Please let Mr. Smith know that he has items awaiting pickup.
Anyone else have any ideas on what you could do with such a system?
I'm going to start serious research on this idea. (Even some market research to see if the retailers would even be interested, though I don't see why they wouldn't be.)