Recycling
The feedstock for these machines generally needs to be very pure, so recycling is still going to need a factory or some sort. Once the whole thing ramps up, I think this will be a major part of the market.
Send us your old prints and we'll send it back as feedstock so you can make something new.
I guess as we get further down the track, the recycling process will be miniaturized so we can have our own, but that's going to require the economies of scale that we see in the PC industry.
Thinking about it, the PC revolution is probably a good model for what we'll see with 3D printing. First the geeks and the curious hobbyists get into it with the devices from this article which are much like the sort of "personal computers" you could buy or build back in the late 70's. Later we'll see some standardisation, more reliable and versatile printers that don't need as much skill to use, much like the original IBM PC and it's clones.
Can't wait. This looks like a great toy to keep me entertained in my retirement years.
