“There’s something happening here, what it is ain’t exactly clear…”
Mass production of goods is horribly inefficient, and hopefully soon it will be antiquated.  Instead of goods being sold, ideas and designs will be sold in a digital marketplace.  People will be able to purchase design files on the web, download them, and then print them on their 3D printer.  It will be a monumental shift in humanity as the agricultural, industrial, and information revolutions that preceded it.  I like to think of it as the Sustainability Revolution.  For the first time, production will be match exactly the demand.  No more waste, no more inventory rot, no more greed or wars resulting from imbalances in supply and demand.  One day “Made In China” will give way to “Made in the Parks Family Garage”
Of course, the shortsighted will complain about two things.  First, 3D printers will be horribly expensive for any individual to own.  Second, how will anyone make a livelihood when the threat of a design being pirated and put on the Pirate Bay is very likely.  
Well, curmudgeons thankfully tend not to be students of history and are rather myopic in world views and ignorant of technology.  Let’s first address the issues of 3D printers.  And to do so, look no further than the device you are undoubtedly reading this very blog on.  Putting aside the abacus as the first computing device, the modern computer really had its roots in the World War II era with monstrous machines such as the ENIAC and UNIVAC.  And look at where we are less than a century later.  When you couple this with the fact that technology advancement is exponential vice linear, than we will accomplish twice as much in the 40 years than we did in the last 80 years.  Consider the fact that today, you and I can buy a 3D printer from MakerBot Industries for just over $1,000.  So just imagine what will be possible in 5 to 10 years.  Technically and financially the notion of a 3D printer in every home is very achievable.  I recognize and will address the topic of the consumables that will be required to feed these printers down below…so more to follow.
Conveniently enough, the MakerBot model also lends us insight into the second issue that curmudgeons will undoubtedly raise and that is profiting from one’s design.  After all why would anyone waste time and money creating designs that could be very easily pirated and given away for free via Pirate Bay?  The MakerBot itself is open source, in other words the design specs and software that drives it freely available for you to copy, redesign, re-engineer and create your own product.  In short you could build and sell your very own, self-branded version of a MakerBot.  In other words, there is nothing to be stolen because it is already given away.  All that is required on your part is that any improvements or changes you make have to be offered back to the community.  Call it communityism.  The MakerBot itself is also built upon the open source Arduino microcontroller platform.  It’s open source building on open source, to create new products.  And guess what?  Everyone profits!  It probably defies the basic logic taught in traditional business school but it works.  And this is the future.  And what we are finding is that people are loyal to brands they trust, thus a free and open market takes care of the cost-cutting, cheap knockoff brands that creep up every now and then.  People want to buy from the original manufacture or designer (or at the very least a reputable redesigner) because they understand the act of buying from a trusted source is an insurance for themselves.  If you buy from the original you are increasing the likelihood that if you run into problems you will be able to get support since the company will still be around.   Additionally you are enabling them to iterate and improve their products and introduce new ones to the market.  And when you have a lot people supporting one company or family of products you begin to grow a community where your consumers are helping each other as well as padding your pocket by purchasing your good.  It become a multilateral symbiotic relationship between designer, consumers, and designers who build off your original products.
So to brings this full circle, we will soon live in a world where I will buy a design for shower curtain hooks, download them, make some custom alterations that suit my needs and then print them out and viola I have my shower curtain up.  And not only that I can take my custom design and put it back out into the market via services such as Thingiverse to make profit!  I firmly believe that while shower curtains may be the start, that we will one day be able to print parts for just about anything.  Imagine printing out Lego-esque blocks to build the body of your car.  Download a design you look, make customizations to color and design and print it out.  Imagine the possibility of having a new car every few weeks by simply printing out new car bodies you bolt on to your standardized chassis.
No doubt though, we aren’t there quite yet and there are significant technological advancements need to really be able to do this on a wide scale with products as complicated as a automobile.  Current 3D printers rely on an extrusion process of plastic that comes to you in large spools.  Thus currently we are limited to products that can be produced with only plastic.  Which is actually a lot of stuff when you come right down to it.  Put it doesn’t solve everything.  So as we move ahead in personal manufacturing we will have to solve the problem on being able to work with other materials or invent materials that could be as hard as steel but as easy to extrude as plastic.  In the interim there is the potential to combine 3D printing with laser etching.  There is also the tantalizing prospect of “printing”your food.  Will it be possible to extrude together various proteins that result in delicious meals?  The last problem is how to deal with getting the raw consumables to our homes to do the personal manufacturing.  Perhaps that will be the only thing Wal-Mart sells in the future, spools of raw materials.  Or perhaps just as a company delivers propane today, the raw ingredients used in the personal production will be delivered as needed.  Consume less and you can wait longer between fill-ups.  And when you are done with your current car body, simply recycle it and receive a credit on your next fill-up.  Make sustainability profitable.
Whatever the challenges certainly they are not insurmountable.  There are just too many real benefits that come to all of humanity in that we will be able to fundamentally change how we deal with the manufacture, transport, and sale of consumer products.  Less need for shipping and warehousing cuts down on consuming energy.  Combine this with a targeted geographical renewable energy solutions, and viola, we have one pretty darn great world for our children to grow up in.

EDIT:  I was going to to use the famous quote often attributed to Thomas Watson of IBM (“I think there is a world market for maybe 5 computers”) to address the acceleration of technological and how we tend to underestimate greatly what is possible.  But it turns out, there is no conclusive evidence that he actually used those exact words.  Ahh, if we only had YouTube back then!