No need to wait for 3D printing, last night I was reading a short story [1] in which the players in an ARG earned experience points via the hand delivery of items from one player to another in the real world forming an alternative delivery system from the postal carriers.

Similarly, in Daniel Suarez's Daemon [2] he describes how a series of net connected people pass around individual parts that they have no idea the purpose of until they all get delivered to one guy who assembles them into a gun.

1 - http://www.amazon.com/Metatropolis-John-Scalzi/dp/B0058M5ZJ6 - "The Red in the Sky is Our Blood"

2 - http://www.amazon.com/Daemon-ebook/dp/B003QP4NPE/

In Daniel Suarez's Daemon (and sequel, Freedom), a dying programmer develops an AI that maintains a fair economic system for its participants, and harshly punishes violators. Great read. http://www.amazon.com/Daemon-Daniel-Suarez/dp/0525951113

I was hoping his next book was out. If you're looking for a interesting book to read that while technically futuristic isn't stupid, definitely check out Daemon. http://www.amazon.com/Daemon-Daniel-Suarez/dp/0525951113