I have no idea of the relative
> popularity. I would have thought salt grinders are more popular today, since
> it seems like Mortons Iodized Salt in the blue container was the only
> commonly available choice years ago.

Maybe it depends where one lives. In California in the 70's & 80's
grinders and salt for them were readily available. I was accustomed
to buying a certain kind of salt for the grinder, perhaps it was a
rock salt, but then moving to Hawaii and Washington state, I found it
difficult to find the salt for the grinder and started experimenting
with other salts, none of which I used the grinder for.

I wonder what I used it for, but I just read that there is an Italian
salt that one uses for bruschetta, and the reason the grinder is
better is that it is more controllable as you grind it over your
bread. Sounds reasonable.
Bon Appetit.
Dee