3D printing will absolutely revolutionize the manufacturing industry. As mentioned before, this technology is just in its infancy now. The printers themselves are rapidly evolving to produce higher resolution parts with greater accuracy, and more sophisticated materials are becoming available almost on a daily basis. This will enable 3D-printed parts to go right into service with very little, or no follow up finishing. It's already possible to print complete assemblies with moving parts, which will move products to the marketplace much faster and with fewer manufacturing steps.
One of the biggest areas of manufacturing to be affected will that of injected-molded parts. No longer will expensive tooling be required to make parts that are found in just about every consumer product on the market. Prices for these items will fall because expensive tooling will no longer need to be amortized into the piece-part cost. Whether you're making 10 parts, or 100,000, the cost just boils down to material and time on the printer.
Audi recently announced that it will start using metal-based 3D printed parts in its vehicles in the very near future. Airbus is moving in the same direction, and GE is already using 3D printed parts in its jet engines. GE is also working on a miniaturized 3D printed steam turbine that will be used for water desalinization.
Read about how 3D printing is already being used in aerospace here:
Aerospace - 3D Printing Industry