I think they will take awhile to hit the quality most people want. Right now the affordable ones like the Maketbot really are terrible resolution. However I do forsee a day when just like the color laserjet printers were once tens of thousands now you can get them from several companies for a few hundred. I figure 3D printing will go the same way unless some regulatory bullshit comes down on them(there are big companies in huge amounts of fear of 3D printing, Even though it will revolutionize how people get small widget parts).
After all NASA has printed functional rocket parts, However to get a NASA grade 3D printer you would have to mortgage the whole neighborhood.