For historical fiction - I think sometimes people (I'm not referring to anyone in this thread) need to remember that it is exactly that - fiction.
The great Edna Ferber made reference to that in the preface to one of her books - I think it was Cimmaron. She acknowledged that a couple of the dates she assigned to real events were in fact a year or two off - but she had to do it that way, in order to make the rest of the story fit. She did have a rather creative term for nitpickers who would constantly let her know how "wrong" she was (I gather people did this by snail-mail in the 1920s and 30s) - unfortunately I lent out my copy so I don't recall exactly what it was.
More generally -- some seeming anachronisms, too, I feel can be given a pass. This in the interests of making the narrative flow more smoothly, and be free from distractions over trivial matter. As Margo says in post #3, "I can live with using modern language (after all, people would have used what was, to them, normal, colloquial language so it gives you the immediate 'feel'...)" Other things too: I was reading a while ago, a murder-mystery novel set in the 7th century A.D., in what would later become France. In discussion between the characters about the logisitics of their travels, distances are spoken of in terms of kilometres. Initially, this grated on me; but on reflection, I feel, simpler to have it thus: let it be understood that the characters were really talking about whatever the measures of distance were, in France-to-be a millennium and a half ago -- better than the author using whatever the real term was, and then having to fiddle around distractingly with footnotes...
In the "minute nitpicks" league: one of mine came to mind, with the discussion involving Paullina Simons's "The Bronze Horseman". I recall from the sequel to that novel, in which Tatiana manages to get out of the Soviet Union and become resident in the USA -- she has for some reason, to travel by rail from New York to Chicago or some similar journey. The author has her dealing with "Amtrak", to undertake this journey. This made me wince, because this action is happening in 1946: Amtrak, the US united passenger-rail authority, did not come into being until 1971. Tatiana would have dealt with private railway company / companies. I being a railway nut, would be likely to be more upset than most people, by a bad anachronism in this sphere -- it's a pretty tiny and obscure thing, and I'm ready to accept admonitions about getting a life...