It’s not the printer, it’s the materials. Laws of physics (mechanical strength of a part that is produced layer by layer), and Chemistry (properties of the material itself). This will continue to improve as more and better materials are developed and adapted for 3D printing. Or as new methods such as selective metal sintering are brought to the price point where they are competitive.
Or when people realize that a 3D printed part could be used to make metal cast parts.
Or when they realize it’s just about as easy to have a home CNC machine the damn part in the first place and forget all this 3D printing hype that makes for good scare tactics.
But right now, the state-of-the-3D-printing-art is a gun that blows up after 6 rounds: http://www.dailytech.com/3D+Printed+Gun+Fails+after+Six+Shots/article29339.htm