Predicting the future can be straightforward if you follow certain rules. They are more guidelines than rules, actually, as I will expound upon later when we get to discussing one of the pioneers in this field of prognostication, that well-known 16th century writer of entertainment fiction, Nostradamus. One approach to this art of prediction is to apply certain constants in human nature to otherwise unrelated trends. Whatever it is, you can be pretty sure that people will find a way to apply it to the themes of sex, killing people and stealing. Its almost guaranteed. Airplanes? Internet? Automobiles? It doesn't matter, people will use them for sex, killing and stealing.
So lets apply this approach to the emerging field of 3D printing.
3D printing is hot, it is not only in our future, it is in our present. People are printing out parts for their vintage cars already. As always it helps to have a lot of money because then you can have access to printers that can print stuff that is really hard and very precise, but even the cheaper printers are fun.
So, first sex, then killing, and finally stealing.
In the area of sex and 3D printing an obvious approach is to consider the impact on sex toys. I know very little about sex toys I admit, but I once employed an animator who was very involved in collecting items made in Bakelite (the classic original plastic) and other plastic items on Ebay. She was particularly fond of Hello Kitty sex toys. If she had a 3D printer today, she could print her own and possibly reveal a whole new dimension to her already formidable creativity. So it is easy to predict new and creative forms of sex toys unleashed with 3D printing, no problem.
How about using 3D printers to print semi-automatic weapons? Again, no problem, it is already being done. See this excellent link to a hardworking pioneer in the field and his discussion of how the topic is regulated on various 3D printing sites.
As a technical addendum to this example, I should point out that the history of modern weapons since before WWI has been to design a very reliable, accurate and functional weapon that can be produced in quantity. The standard infantry weapon of most modern armies can be made out of a remarkably few pieces of stamped metal. The author of the post referenced below, as a student of firearms, was well aware of this.
"Gunsmithing with a 3D Printer, Part 1" on haveblue.org
Finally, how do we use 3D printers to steal money? One way of course is to use the weapon you just printed to rob a grocery store. Simple, clean, and yet very stupid. After armed robbery the first approach that comes to mind is the low-quantity counterfeiting of valuable art objects, collector's items of one type or another, including objects from antiquity. The feasibility of this depends on how the choice of materials evolves with 3D printers and how clever people can be with emulating the characteristics of objects made of other natural materials as well as how clever they can be in emulating that feeling of antiquity at the surface of the object. Of course none of this would fool an expert, we are just talking about fraudulent items on Ebay in this scenario, I think. It would take a very precise "printer" indeed to sculpt out of metal a simulation of a rare Roman coin, perhaps a counterfeit Sumerian cone would be more amenable, though less valuable on the current market. But whatever the future of art fraud is with this technology, I have no doubt that the biped mammals will make me proud and find ways to use this technology to steal.
Only time will tell if I am right or not, but I am optimistic about this.