I think 3D printers are firmly in the "Linux desktop" stage for now. You will hear it's revolutional arrival announced every year, but it will never materialize.
I'd put them firmly in the same stage that computers were back when you had people in their garages soldering together homebrew computers.
Computers had evident uses people craved for even when nobody had one at home: coin-op arcade games for example drove huge crowds. Writers used electronic typewriters with small displays and would be better off using an editor program. And a spreadsheet was a killer app for any small office -- they already used calculators. Add communications and entertainment to that (mail, chat, www, video) and computers had tons of killer uses.
A 3D printer is a one trick pony. It merely prints stuff. (Well, a computer is a one-trick pony too, it just "processes information", but in the realm of information this amounts to infinite possibilities).
People that like tinkering and DYI will love one -- but they are not that many. The general public, not so much.
They can create any thing/part they want themselves? Well, the thing is, generally they don't want stuff created. And when they do, they can also have some factory create them somewhere and buy them. And even if they needed something extra-custom, they could order it to a 3D printing shop down the road, and be spared all the trouble of owning a 3D printing, managing supplies, learning the software, etc.
The analogy with the home computers is interesting, because people are even scaling down on buying home computers. The general public finds that the limited stuff they wants to do, they can do it with a smartphone and a tablet (and maybe an ultraportable, for the more needy).
Heck, tons of normal people don't even like owning 2D printers (and have always had lots of problems configuring and operating even them, as evident by any support forum).