They don't know it but they likely have a motor someplace in their house that runs at the speed it does because of frequency. They are ignorant but it affects them.
I think fans will likely be the last devices which care about frequency.. but new ones are often 12V/24V-based, with a little step-down modules.
You might be able to trip up a fancy soldering iron where loop bandwidth is intentionally maximized, but I still suspect the first thing to go would be the magnetics on anything with a transformer.
Yes, but not for the reason you'd think: 50 Hz magnetics have to be physically larger to work (peak flux density for a given current is higher), and magnetics are so big and heavy that they're not designed with much margin. So 60 Hz transformers will often not work at all at 50 Hz, and 50 Hz transformers will sometimes perform pretty badly at 60 Hz (though also sometimes going this direction works fine).
I’m seeing more and more EC motors in commercial applications, for things like 2-3 HP fam motors and pumps.