If we think about the current state of 3D we are quite simply using more 3D now than ever before, hollywood films have totally absorbed the medium as a production tool for blockbuster films, product designers are using digital in every aspect of new product design and the applications that support all these people from professional to amateur are getting easier, faster and more approachable to learn. For example, Autodesk now has offers 3DSMax and Maya as their entry level 3d applications, and although very deep applications in terms of functionality, they also are supported by a huge network of budding 3D artists on such sites as CGsociety. The line between amateur and professional is much less now than it may have been decades ago where you might need a degree in either engineering or software to understand 3D design.
This leads me to believe that learning, and using 3D applications now, as well as finding great 3D assets and designers is far easier than ever before and will continue to rise, as more jobs look for these skills and people learn them whether for career options or personal pleasure. Just look how quickly the video editing industry changed as more people started to use video editing software on their home computers. If this adoption of 3D proves to be true then why not in the future wouldn't people start to design and even print, their own products. They might even be able to join a community of designers and even if unskilled in the actual design, maybe they could download the "blueprint" models and just hit the print button. It seems very likely that crowdsourcing efforts could easily create very usable functionally correct objects. Now of course, the objects are going to be simple at first. I could easily imagine a toothbrush, or computer mouse already being possible. Really the only missing parts are the electronics, however with a network of "object creators" all that would be needed is templates and purchasable packs of parts to transform you dead 3D printed object into a real working tool. After all I pull apart my electric toothbrush and the only part I couldn't 3D print is the battery.
Todays social networks show that people like to create and customize their own creations. iStockhphoto is testament to what a good crowdsourcing model can produce. High quality very acceptable creative work. 3D would fit nicely into these existing models of crowdsourcing and social networks, with the right motivations and rewards I think 3D artists and engineers would be glad to share their work. Their is no reason that I can see that once the cost of the 3D printing hardware comes down and the materials available allow you to "bake" them or pick harder materials for regular use that this couldn't take off as the next big phase of digital printing.
You could even, make the jump of saying that if the right materials are discovered that the objects could utilize the fact they these objects are easy to create and don't last forever. Maybe they should be made of some kind of biodegradable material. Use it a few times them as it starts to degrade, put it in the compost and print another one. Nothing I like more than the idea of sustainability.
So of course this is very future thinking, the printers are not cheap, the materials I am sure are equally expensive and probably not bio-degradable. The machines require a dedictaed room and you need to be quite a 3D wiz I am sure to make it all work. But then once upon a time the humble computer required a degree in computer science and a dedicated room to house it. Look how far that has come.....