So you want to print your own circuits? The BotFactory Squink has you covered. It lets you print circuit traces on stiff and flexible materials. Squink lets you lay down solder paste or conductive glue on boards with its extruder toolhead. The Pick & Place toolhead has computer vision to correct errors.
Squink has an ARM Cortex-A8 processor with two real time controllers, SIMD and GPU acceleration. It supports max circuit size of 6″ x 6″. This seems like a wonderful prototyping tool, but it does not come cheap.