I am trying to think of some but I can’t. Something that you could tell to the common layman that would pique his interest. Most of the applications are pretty esoteric, things like MRI machines, SQUIDs, lossless microwave antennas. The closest thing I could think of as an exciting application is MagLev trains. But there has got to be something better then that!
What revolutionary and exciting technologies would room-temperature superconductors make possible?
There’s an article on it this month in one of my magazines, but I can’t remember which one – Scientific American, American Scientist, Technology Review… One ‘a’ those kind.
NMR machines? Not sure that it’s any more fun than trains, though.
Well, the obvious application is long-distance power transmission. People anywhere in the continent could use power generated anywhere else on the continent, with essentially no cost for the transmission (other than the cost of putting the infrastructure in place to begin with). You wouldn’t need to transmit it at high voltage, either, which means you could make the infrastructure a lot cheaper and safer than currently, too. You could grab a bare superconducting wire serving an entire city without harm, as long as you didn’t break it.
But the voltage would have to be compatible with existing devices, which means a given conductor would need to be 120 VAC, 240 VAC, 600 VAC or whatever relative to earth ground. I wouldn’t want to touch such a conductor unless I’m extremely well isolated from earth ground. 
As far as superconductor applications go, engineers have recently been able to build microwave filters using superconductors with characteristics that are impossible to achieve with conventional microwave filters.
You could transmit power long distances at any voltage you’d like; you just step it to whatever voltage is appropriate at the end of the line. This is already done anyway, with long distance power lines, albeit for a completely different reason. Of course, you’d probably still want to hide and protect the line, since fools are so ingenious, but it would provide one more layer of safety.
The Large Hadron Collider will use superconducting electromagnets to steer opposite beams of protons around a 27km circular path, and accelerate them to nearly the speed of light, so that they collide with such energy that it will simulate the conditions found in the universe a tiny fraction of a second after the Big Bang.
I’d call that pretty exciting.
True. And you bring up another interesting point: can transformers be made more efficient using superconducting materials? The I[sup]2[/sup]R losses would certainly go away, but what about the eddy current losses? Would constructing the laminates from superconductors eliminate eddy current losses? I don’t know. Perhaps Q.E.D. could chime in.
How close are we to achieving room-temperature superconductors? Are researchers even sure they must exist or be possible?