If this post's headline seems awkward, it's because I can't quite find the right words to describe the service.
"What happens to the music bits today will happen to the chair bits tomorrow when you are able to download the arm-rests from Ikea and the upholstery from Crate & Barrel, mix them up and print them out."
This sounded a bit too sci-fi even to me when I posted it a couple of years ago. Today, I found Ponoko.
Ponoko (about) is for physical things what Lulu is for books and what CafePress is for t-shirts. You create a design for, say, a chair, upload it to Ponoko's site, and list the chair for sale. When someone likes your chair and pays for it, Ponoko laser-cuts the pieces out of a range of materials, packs them up and ships them to the buyer. Or to you, if you want to assemble the pieces first. You can buy product plans created by other people and, depending on the license, customize them to make and sell something new.
You can see, of course, how something like Ponoko is a great fit for the 3D interface of Second Life, which is all about people designing 3D models of stuff, or Google Lively (read AdLab's first impressions).
To throw in somewhat similar services I discovered while looking at Ponoko: FigurePrints makes custom WoW models, ShapeWays does rapid prototyping on demand, and a few others mentioned in the previously posted stories here on AdLab.