The old schoolroom certitudes about grammar and usage that many of us were taught have come under fire: from linguists who question their validity, from lexicographers who record widespread usage that flouts those rules, and even from prescriptivists like Bryan Garner who call them superstitions.
Those of us who edit have to watch and monitor the development of the language. Singular they appears to be gaining ground. Whom seems to be on its last legs (though Geoffrey Pullum suggests puckishly that there may be a biological advantage in using it). Whether to stick up for or abandon a long-standing usage is a delicate point of judgment.
Thus on March 12 I will be conducting an audio conference for Copyediting, "Judgment Calls," in which I will address a number of these thorny points of usage and offer advice on how to make reasonable editorial choices.
I not only hope that you will sign up for what I hope will partake of conversation as well as monologue, but that you will also offer suggestions about points of usage that you find vexatious. Be assured that I have a list of my own cued up, but I think the conference will be more productive if it takes account of the issues you identify from your own work.
Feel free to make suggestions in the comments, or to write to me directly.