3D printing is going to change the way we make, distribute, and use physical goods. This video shows it's not just about glasses. Complex mechanical systems can be printed at will from a design file.
I found this video from Emmett Lalish about the 3D gears he prints so fascinating I had to share it.
If this doesn't convince you that 3D printing will change many of the assumptions we have about products and physical things, then you're not paying attention.
Companies traditionally design a product, contract with a factory in China to manufacturer it, ship it, market it, etc. With 3D printing becoming more and more capable, companies will just focus on designing the product, marketing it, and selling it. The product won't be physical, it will be the design in a digital format that will allow the customer to create it when they need it.