I agree, there are way too many tchotchkes on sites like Shapeways and Thingiverse, and way too few useful products. I wonder what the first "killer app" for 3D printers will be. That said, I think they are already practical for prototyping or DIY tinkering projects.
I think digital-to-physical manufacturing is so much bigger than 3D printing. http://fabsie.com/blog/3d-printing-vs-3d-cutting/ and that CNC routing (3D cutting) is likely to find killer apps far faster than 3D printing is capable.
Not in the eye of the mere mortals. Those 3D-cutters are just something that exist somewhere in a factory, could just as well be a black box. Most couldn't care less, you can't own a 3D cutter, unless you are really dedicated. Anyone can own and tinker with a 3D-printer.
Even the difference of being able to play or rent a 3D cutter at work or through some service, or iterating something at home that you've made yourself, where the only real cost to it is your time spent having fun, is game changing.
If you restrict the debate to the maker movement and people at home owning machines, I completely agree that the average joe can't own a large 8x4 3D cutter and never will, yet they can own a basic small format 3D printer.
But the average joe is unlikely to own a kiln either and unlikely to own any form of industrial pre+post-process. Disruptive manufacturing is my main interest as well as the new models of digital distribution. I believe the home will be an extremely limited means of production, but indeed a computer controlled plastic extruder (3D printer) will be an accessible technology many can own.
The killer app could be 'parametric' thereby needing digital-to-physical manufacturing such as 3D printing. For standard static items made in plastic, there are no signs what so ever that injection moulding will become redundant any time soon.
In the case of normal printing, the desktop printer didn't kill the rotary printing press, (althought the internet digital press may). Desktop printers and rotary printing presses exist for different use cases. Printing notes to red mark or travel tickets vs. a glossy magazine/newspaer. The relationship is akin to 3D printing plastic / injection moulded plastic and will likely have different use cases.
