I grew up in Seattle in the 1960s hearing only "Holy Spirit".  I did see "Holy Ghost" in some older books and Missals that were on the hallway bookshelf in my home and understood that to be the way people spoke in the "olden days" when they also said "thee" and "thou"--at least that what I thought.

An elder friend of mine told me that they switched from saying "Holy Ghost" to "Holy Spirit" in the mid to late 1950s where he grew up (rural Indiana).  He said that the reason they gave (he was old enough to ask why they were changing) was that ghosts are scary and they didn't want people to be scared of the Third Person of the Blessed Trinity.  He told me that he thought that was a stupid reason at the time because he had never been scared of the Holy Ghost!  (So Myrna, it wasn't just where you were growing up!)

It is also true that I've seen the two terms used completely interchangeably--even in individual books published before the Council; though I can't say that I've ever seen the term "Holy Ghost in any book (other than reprints) published since the Council.

Today, I consider these terms to be more political than religious.  People who usually use "Holy Ghost" are usually traditional Catholics.  People who always use the term "Holy Spirit" are almost always Conciliar Catholics, Protestants, or non-religious English speakers.  I can't say that I've ever met anyone who usually says "Holy Spirit" but sometimes says "Holy Ghost".  The term is simply a good way know quite a bit about a person's religious beliefs.

The statement that all Trads use "Holy Ghost" is sadly, not accurate. I have been in FSSP parishes where all the faithful, and even the priests, say "Holy Spirit."

Most Indulters also say "Holy Spirit."

You say that not all Traditional Catholics use "Holy Ghost" and then tell us about Conciliar Catholics who say "Holy Spirit".