I don’t know if you have noticed, but printers nowadays work. In the last few years, I’ve set up and used a bunch of printers and it has been very much a plug-and-play experience. Just connect the printer to the wireless network and you’re ready to print. I use OS X, but I hear it’s the same for my Linux-using friends. I’ve also successfully printed from my phone. Heck, I even scan wirelessly from my laptop!
Ink is still atrociously expensive and runs out immediatel, and printers are getting less and less important as people move away paper. Still, it’s cool that we’ve finally made the printers work. They used to be such a pain.
For other things that have started working in this millenium, see Dan Luu’s article What’s Worked in Computer Science.