This is footage from the what was apparently the first live concert played completely with 3D-printed instruments. From the little bit we can hear, it doesn't sound as bad as you might expect!
The show, played by students from Sweden's Lund University Malmö Academy of Music, featured a band with two electric guitars, a drum set, and a keyboard. They were printed by Olaf Diegel, a Lund University professor, and seasoned 3D-printing pro. He's been fiddling around with 3D-printing since the '90s, and has focused on instruments quite a bit, most recently completing a 3D-printed saxophone.
In this clip of the concert, the instruments don't exactly have the full assault of the sound of regularly crafted guitars and drum sets, but it doesn't sound terrible. Of course it's worth noting that electric guitars and basses get almost none of their quality from their bodies. And while the band is made up of all 3D-printed instruments, not every component of each instrument is 3D-printed; there are no plastic strings or pickups here.
The attendance was pretty sparse, but by George, even the Rolling Stones had to start small. And maybe someday you'll be able to print up a bands' worth of instruments in your own garage. [3D Print via DamnGeeky]