What's the difference between a graphic designer and an artworker/Mac operator/production artist? Is one a subset of the other? Do they overlap? Are they industry-specific terms? Are in fact artworker/Mac operator/production artist not synonymous?
A Graphic Designer is one who is working on the conceptual/strategic side of things.
A Production Artist is the one that takes the conceptual/strategic solution and and implements the mechanical files for the solution.
You'll typically find Production Artists in ad agencies where they'd be working under the art directors. In design firms, the graphic designer is quite often also the production artist.
There is a lot of overlap, and this is probably better explained with a Venn diagram than anything...
"Graphic Designer" can really be applied to any of those jobs, if only because basic knowledge of graphic design—to create and combine words, symbols, and images to create a visual representation of ideas and messages—is needed to do them, and in casual conversation "graphic designer" is much more self-explanatory than "production artist." The specific titles really apply to specific jobs within the graphic design field, and are in variably synonymous across the industry as a whole.
The one caveat I see is "Mac operator" in that, while I haven't heard it in a very long time, my experience was that it typically applied to someone who took content and art and poured them into templates, and had no concerns about the actual design besides reporting where the design did not meet the needs of the content and elements.
In job ads I see these days, there usually is no difference between Production Artist and Graphic Designer. I see many Production Artist job ads that want you to be an expert in Adobe software, along with having web coding expertise, etc. It seems that they may use the Production Artist title to keep the salary low.