I did work for a small community college back in the 90s that had expanded their building multiple times since the 70s. The electrical potential between different parts of the building was significant enough to make wired Ethernet unreliable. (I never did understand why this was-- multiple electric service entrances with separate grounds, I assume.)

Because of this they were an early adopter of fiber-based networking. I remember being wowed by ATM over fiber running between closets at a blazing 155Mbps (with tons of 10BASE-T clients connected to FORE chassis switches).