Hi,
My name is Lukas.
I've sketched and drawn physical gadgets since I can think of.
Somewhere along my way in English education (I'am an Austrian) I guess I was around 17, I got to read an article about
absolutely beautiful nano-machines of this kind:
http://www.zyvex.com/nanotech/visuals.html
http://www.imm.org/research/parts/
If you ask what that has to do with 3D printing then please be patient.
I didn't even know of the existence of 3D Printing at that time.

I guess I first learned of the existence of 3D printing around the time shapeways popped up.
I immediately knew I had to try it out and started 3D printing with this dutch 3D printing service.
After I've tried all the major materials which where available back then
I found it to be rather expensive and thus only usable for jewelery and only a vew other things.
This brought me to the decision that I finally want to buy my own personal 3D printer kit.
At that time I was fortunate to be late enough that the the Ultimaker was already in pre-order state.
Since I own it I put it to good use as you can see here.
http://www.thingiverse.com/mechadense/designs

But thats not the end of the story.
Remember those "Diamondoid Molecular Machine Elements" I've mentioned before.
Completely unrecognized by the general public (at least in my part of the world)
atomically precise nanotechnology is slowly but certainly progressing to a state
where atomically precise printers (for non metallic elements) become possible.
A recent example of the progress can be found here: http://wyss.harvard.edu/viewpressrelease/101/
Further stages will quickly switch to crystalline carbon and silicon as building materials.
Don't be mistaken - atomically 3D printing devices will not evolve from current day 3D printers but come from labs that combine
bottom up and top down nanotechnology.
Even though they'll emerge from rater secretive parts of the technological development (if sensibly designed) atomically precise 3D printers (in the second or third generation) will share the open spirit in that they will be copyable with just a bit of welding gas as the only necessary resource. Later just sun and CO2 may suffice. Those printers will come in all sizes (think key-chain pendant) and spread over the whole world in no time.
Every one of those key-chain-pendants will be a seed - capable of rebuilding the whole word even after a 3rd WW (not judging it's probability here)
Just to remind you that those won't be almighty wonder-machines: Food will not be printable this way as you will find if you decide to look further into the details.

By the time this technology will arrive we'll already will have a quite vast library of all sorts of stuff.
But beside Macro-products the nano-machine-elements must be designed too.
Here I've written a tutorial about how to convert designs for future nano-machines to
something that can be printed for presentation as a model with current day 3D printers.
http://www.thingiverse.com/thing:13786/#instructions

In our future the whole world around us will be programmed and often packaged with it's code.
Today I do mainly use OpenSCAD since for me its the most easy to use and practical software there is at the moment.
But for diverse reasons I'd rather like to see some cross of those two:
https://github.com/colah/ImplicitCAD (plus quick preview)
http://sourceforge.net/projects/mole.../NanoEngineer/

I plan to publish some thoughts of mine about atomically precise 3D printing here:
http://scriptogr.am/mechadense

Some literature about atomically precise manufacturing - If you're interested:
http://www.amazon.com/Radical-Abunda.../dp/1610391136
http://e-drexler.com/d/06/00/Nanosystems/toc.html

So in summary what establishes my interest for 3D printing are my need to get those gadgets out of my head and my motivation to showcase detailed concepts for components of future atomically precise (AP) systems. If you've not already known about AP printers it I hope I could spawn your interest.