Essentially, barriers to entry become lower (start-up costs and time to pay of debt). In that case, competition for customers becomes fiercer, forcing many established companies to shed variable capital costs (eg. Labour). The flipside is that products may become cheaper - 3D printing is at a stage where only the most basic techniques are widely available. Makerbot, RepRap use ABS and PLA plastics and additive techniques..CNCs and draftbots use drills, wood and ink....but overall, there are major limitation in what they can make. So perhaps jobs will be lost in just particular sectors.
Intellectual property of physical products are threatened - what has not been disclosed in the news about 3D printing is that 3D scanning is getting better and cheaper too. I am currently working on my own design for one....costs so far: 45 bucks. Simplistic designs can be copied and reproduced - toys and games. Open Sourcing of designs along with community effort to improve said designs have made Thingiverse and Shapeways the touchstones they ought to be. The problem is that existing designs and all the hardwork involved in their R+D are threatened. Why make a product when you can copy someone else? Why make a product if I can't make money of it? Well, there is no replacement for good quality....and that still matters...let me illustrate this.
Imagine a world where there are thousands of 'print shops' that can make virtually any part with any material. A part blows up in your car, the master cyclinder. You reconstruct it, you scan it, send it to the shop, and they use laser sinistration to make the part. Money and time is saved. Quality it may not - that is the catch with 3D printing and scanning for the next decades...low quality. And the only thing holding the bottom of any industry is doing their job right..producing quality products.
Lets talk about the Dshape's impact on the US construction industry which is made up of 710,307 companies and contractors, makes 1.2 Trillion and pays out 250 Billion to 7 million employees. The Dshape can make a lot of basic masonry as well as building structures. It also needs 2 people to run it and is completely automated. For concrete makers and users, this is a serious threat. Yet for carpenters, landscapers and every other industry involved with finishing, there is a big advantage. They will have plenty of business to finish the shells of these buildings. Not only that, carpenters can use cheap CNC machines to produce customized products. Landscapers can make customized garden ornaments with the Dshape. Most importantly, it reduces costs of house building. Arguably, it opens up the possibilities of design. As Thingiverse and Shapeways have demonstrated, Open Source and 3D printing are meant to go together. Large Scale 3D printing of buildings will have to step up and change the Construction Industry and bring it into the Open Source fold.
Open Source changes the mode of work, and i believe it makes for more productive workers. I certainly believe that industry will become even more diffuse and atomized, which can often strengthen an industry rather than weaken it. For the construction industry, that could be a major boon.