dunt let the door hit ya on the way out

I'm a little more concerned with why the team that made the plastic gun called their toy the "Liberator"...

I still do....currently building the Tiger 1 model that comes in 100 plus weekly parts...many are metal...and just started the collecting of the bits for the Red Bull F1 car.... both models end up around $2000 -ish ....but you don't quite notice it at $15 a week...

I can think of a million things I could replicate with a 3D printer....but then my hobbies include scratch-building in paper or plastic...all the way up to designing and building my own bicycles [in steel]...

Yes, CNC machining from bilets etc all handled by CAD/computer is where it's at, particularly in Aircraft and Motor Racing....but the concept of actually making multiple 'bits' inside each other via a 3D printer is mind-boggling ...OK, so the whistle complete with ball is 'quaint' but the idea of effectively having pre-constructed components without any facility for dismantling...that's the amazing bit....when all that's needed is an 'exit hole' for the non-printed powder/material to be removed.

I can remember when the concept was Science FANTASY ....then it became Science FICTION...and now it's almost simply affordable kit...

As machines of this nature become more commonplace materials costs will fluctuate accordingly based on demand and supply. In general though, I feel the costs will eventually come down low enough to where it will much more affordable for the everyday person at least in comparison to where it is now.

We technically have the technology to metal rapid prototype on a 3d printer a complete motor assembly that will run, though I do not believe it has been fully attempted (at least in full scale) yet. The cool (and for some, scary I suppose) part about metal rapid prototyping is that you have a metal component, or component assembly that has the strength of a weld throughout it's entirety. Need a new motor for your model airplane? Print one off and install it. Need a new wrench while you're in space, or on another planet's colony? Print it off in about thirty minutes.

You're assuming that the production market for these materials is already saturated. As demand rises more manufacturers of these materials will appear which will drive competition and the costs will be reduced. As the industry drives forward and demand increases, producers will rise to take advantage of this demand and the costs will go down. I am fairly certain that there is a large enough profit margin is already instilled in these materials that the cost can significantly be reduced with a profit still being turned.

This is my opinion just as your opinion is yours, but I think you may not fully understand how easy it is for manufacturers to create many of these materials that are used in the rapid prototyping process.

Not quite right....not when the most common 'plastic' on the planet is wood [and glass is a liquid too, btw]

Synthesizing 'plastic' from alternate sources is a lot easier than doing the same for petrol....pure supply and demand will determine how, where and why alternatives are sourced...

Assuming you're talking about laser sintering or similar techniques, the strength is going to be pretty questionable unless you're a skilled metallurgist already and have the facilities to do the work in an oxygen-free atmosphere and anneal it afterwards. At best, it'll still be at least somewhat inferior to casting or milling.

I just donated my MakerBot Cupcake CNC to our local high school engineering class. 

It was first generation and I failed to make a single print with it after playing with it for a year.  The amount of fixes, tweaking, tuning, modifications and technical knowledge/intuition needed to "just use it" made it really impractical for me.

A few days ago I got my 3rd generation Solidoodle printer.  I spent quite some time reading through forums posts on it before ordering one.  Looks to be a little more practical and yes--plastic ain't cheap but I can get 2lbs for  under $50usd and that's enough to print potentially scores or even over a hundred prints.

It does however blow away paying someone to cast molds or make plastic prototypes for you and would be invaluable for a product sales pitch or patent application.

I'm $1600 into the 3D print market and am going to stick with it.  MakerBot opened the door and user experience has made all of the machines progressively better--though you have the learning curve of Sins MP involved in actually getting the hang of using them.

Printing is slow compared to commercial machines and down time for re-tuning, tweaks and repairs is likewise high.

BTW--a hospital just printed a 3d structure matched with MRI images to fit in the chest cavity of a newborn girl with a collapsed chest and un-inflated lungs.  It was made of biodegradable plastic and after implantation she immediately began to breath normally and it allowed her chest to grow into proper shape.

NASA just funded development of a 3D food printer for astronauts so exact nutrients and calories can be designed into each individual astronaut's meals onboard a space vessel.

Food replicator anyone?

Not quite....but can you spell 'amorphous solid'? ....