3DP's a great! They are a lot of fun. And great for teaching kids about Making.
But their current limitations make their applicability pretty limited:
1. Most printers use some form of thermoplastic (like ABS) to actually generate the object. It's pretty weak, especially since the object is constructed one layer at a time, so the bond between layers is not very strong.
2. The cheaper printers (like Rep-Rap and MakerBot) don't cost too much (you can build one yourself with a $1,000 kit), but their precision is not so great. The more expensive ones (like Stratasys and Z-Corp) can easily cost upwards of $15K. Their products cost can easily be $25/cubic inch produced
3. The most interesting devices are using some form of laser melting metals (like Direct Laser Metal Sintering by EOS). The produce very cool objects out of brass, stainless, even titanium. But the machines cost $250K and up, and so the results are even more expensive: a 1-2 lb part can cost $2,000
So at the moment, 3DP's are used two ways:
1. Learning - vast majority of printers are built by Makers to mess around with and to learn, and make cool things that are not going to be stressed too much
2. Rapid prototyping by companies, where the cost is less important than the time it takes to make a physical prototype or a plug mold
I'm working on helping 3DPs break through these limitations
