Unfortunately with all of the interesting possibilities for convenience that 3D printing brings, it also brings a lot of problems and controversy. You could easily 3D print stuff from its 3D model rather than actually buying it from the shops. This means that piracy of physical objects could actually become a problem in the near future. People could start downloading Ikea furniture designs, for example, and just start printing them. No need to go to the shop or pay any money to Ikea, even though they own the design. The only way that currently seems viable is a DRM system for 3D model files similar to the DRM on music, games, and video files. It would prevent users from printing certain 3D models if they did not have the rights to them. That being said I personally doubt that it would take a determined individual any more than a few minutes to get around this DRM. After all it's not like it stopped people from pirating music, games, and videos.
The more serious problem with 3D printing will fortunately not be a problem for a while given the current limited availability of 3D printers, as well as the even more limited availability of sturdy enough 3D printing materials. The problem is that it is possible that some time soon it may be possible to 3D print guns. In fact it is actually possible to 3D print guns now, but if they were made of the currently publicly available materials they would almost certainly explode immediately upon their first use. In fact the world's first 3D printed gun was tested by ATF agents some time last year and it blew up in their faces. Unfortunately they managed to later create a second gun using the same design that was made of sturdier plastics and was able to fire at least 8 rounds.
Personally I'm not really that worried for the time being about 3D printed firearms as bullets still need to be acquired or made in order to use them, which can be very difficult. On top of that there's the fact that anyone using them is fairly likely to have the gun explode in their hands, so I doubt they'll become popular any time soon. As for the 3D printing DRM I highly doubt that it will ever completely prevent 3D printing piracy, but to be quite honest there's nothing quite like the genuine product and at least you're guaranteed a certain level of quality if you do buy from the store. I don't think it will kill off buying most products from the store, but it certainly creates many new opportunities like selling 3D models for things to consumers to print and it definitely would be convenient to not have to go down to the shops when your door's coat hanger snaps.
Sources and related links:
http://www.bbc.co.uk/news/technology-19928502
http://www.dailymail.co.uk/news/article-2507654/The-worlds-fully-3-D-printed-gun-tested-Feds-blows-faces.html