Jim observes that this use is "positive, acknowledging the importance of people who do their jobs diligently."
Camille P used the term pejoratively, but only mildly so, in the sense that merely being good at your job doesn't qualify you to be the boss. Or so I read things. I don't think she meant anything more harsh, though one or two of your other commenters took her meaning to be someone who shifted with the winds.In his email responding to my request to quote him, Jim added: "I never forgot that reference as a testament to the unsung heroes who keep the world running well." (He also recommends the book, saying "an aviation book written by a navigator appealed to me since I'm a former naval flight officer.")