One significant problem with today’s extrusion 3D printers (the kind more people could afford for home, of the order of $2,000) is the output is layered, like a stack of sliced bread, and rather weak in that these slices too easily detach from each other. Almost all samples I touched broke between layers when applying light pressure with the fingers of one hand. Sure, you can design with that in mind, but that is a significant restriction. Wouldn’t want to make an irrigation valve to hold water pressure when you know it has that kind of weakness.
It isn’t surprising, given how the filament of ABS or PLA gets deposited in the XY plane, then after a tiny move upwards on the Z axis another XY plane, at which time the earlier XY plane’s filament has cooled off already.
I am aware that slower runs with more infill produce stronger output. I am not sure how much stronger it would be. At Maker Faire Bay Area 2012 most samples were of the easily breaking kind.
It may be that control over temperature and on and off switching of extrusion will improve in upcoming models. It may or may not become easier to produce output with greater strength of adhesion between layers.
Higher end 3D printers (seen years ago, supposedly our high school has one, of the order of $30,000) use different technology and afaik don’t have the same problem.