I don't believe 3D printing will truly catch on until there are at-home printers that can print in plastic, metals, wood, clay and other substances all at once (for the same object). Once printers can do this, and mix colors, and substances, that's when we will truly see 3D printing take off. You could basically print any household item you need, and it will be as simple as downloading and selecting "print".

What are your guys/gals opinions of when a printer like this will be available to the general public at a decent price?