Aside from research experiments in atomic-sized 3D printing, you might wonder what kind of ultimate 3D printing resolution could be achieved.
Most personal 3D printers use a plastic filament-based process, which really doesn't provide the best resolution. Typically prints are printed at a layer size no smaller than 0.1mm, simply because the visual appearance isn't significantly different when printing at higher resolutions - and those higher resolutions require even more print time, causing wear and tear on the machine.
No, filament machines are not where you'll find the best resolution. Instead, look to resin-based machines. There are a couple such machines entering the personal market, most notably Formlabs' Form 1, which already provide terrific resolution.
But how much better might it get? At this year's EuroMold conference, we took a look at the best output provided by more expensive commercial machines and found the print sample shown above (click for larger view). It's a 3D wax print of several beetles made on a high-end EnvisionTec machine. The detail is incredible, especially when you compare the beetles to the €0.20 coin resting beside the bugs. (Note for North Americans: the coin is about the size of a quarter.)
Eventually personal 3D printers using resin processes will reach similar capabilities, but for now you'll have to purchase an EnvisionTec machine for much more than USD$100,000.