There is an interesting paper posted on the SSRN site by a Stanford law professor who concludes that 3D printing may make product liability suits obsolete. Nora Engstrom points out that product liability laws are aimed at commercial manufacturers, not hobbyists equipped with 3D printers. So if a part made by a hobbyist is somehow "defective" and causes injury, the injured party is basically out of luck. Engstrom also shows that suits against the maker of the 3D printer or against the "digital designer" who wrote the code that told the printer what to print would also probably not be successful.
With regard to 3D printer makers, Engstrom says
"To prevail in such a suit, the plaintiff will have to show not simply that the printer churned out a defective product, but, instead, that the printer was itself defective. And, it’s not enough that the printer was defective at the time it printed the troublesome item—it must have been defective at the time it left the printer manufacturer’s possession and control. If the plaintiff can’t make this showing, a product liability suit is probably a nonstarter."
The difficulty with suing the code designer, says Engstrom, is that, "just as strict liability law applies only to 'commercial sellers' and implicates only those items that are themselves 'defective,' it also applies only to 'products'— defined..... as 'tangible personal property.' And, though there’s some contrary authority, there are strong arguments that code does not qualify."
She sums up by speculating that "courts may well, in typical common law fashion, end up softening lines and blurring boundaries in order to impose strict liability on hobbyist 3D inventors and digital designers, especially if uncompensated injuries mount."
Her essay is free on the SSRN site and can be downloaded here.