. . at least in Southern California. Older houses with 2 wire Romex in particular have no way to ground the box effectively, but if you have the third wire why not just screw it down to the socket where it's supposed to be?

An even more fun problem is buildings with multiple grounds. Ground potential differences have destroyed much network gear.

At a medical testing lab with 24 serial ports, serial ports would start going out after about a day, requiring system turn-off and restart. I said "ground potential". The building's electrician said there was no grounding problem. The multiport board manufacturer said that couldn't be the problem and sent replacement equipment (which did exactly the same thing).

This went on for days. Finally I told the client, "Have the electrician pull a ground wire from the testing machines in the back to the server relay rack or I'm going home and I'm not coming back". This was done (with much groaning and protesting) and the problem was gone.