Today I've mused on historical accuracy in historical novels, and what responsibility I have to the past in my writing. While I was walking up the hill today, just a few minutes ago in fact, I came to the conclusion that my philosophy on the question could, more or less, be condensed into the little disclaimer at the end of game shows and reality TV episodes:
Paraphrased: Certain parts of this show, not affecting the outcome, have been edited for time.
History is (obviously) the framework of historical fiction. As much as I love the movie Braveheart, I recognize that Randall Wallace (the screenwriter) and Mel Gibson dramatically ripped the space-time continuum to tell their story the way they did. That's something I refuse to do. Most of the time, when an idea's popped into my head, the historical event comes first and the story gets framed around it. If the historical timeline has to be skewed or stretched or altered in any major way to make the story compelling, then it's out, and I tell my brain that if it has any better concept set in that era to come back.
Yet minor anachronisms and slight twists are another matter entirely. If I have a character wielding two swords in a time set before the earliest known example of warriors doing such a thing, is that something to get in a stir over? Besides, you have to admit that it's always fun to see someone chopping up his opponents with two blades whistling through the air. On the other hand, there are some things that are seemingly small that really did have a major impact on the time period.
I'm thinking of the stirrup, and when the Franks came up with the concept (no one's really sure when, but I'll draw the line at AD 600), it caused a radical evolution in armed combat. That's major enough that I can't mess with it.
There's a very grey line here, and I'm always asking myself if I'm going too far. After the Battle of Second Manassas (Bull Run) did the Confederates run the wounded back to Richmond in boxcars for treatment? No idea, but the story demands that the protagonist gets back to Richmond, so we'll just assume that they did. Almost nobody will give a damn anyway. There's an eternal struggle between the facts and the story, and I've decided that the story has to win. If I thought that the facts were everything, I'd go to grad school and write straight-up history.
Finally, with historical fiction I think you run the risk of giving readers a false history and making things seem different than what they really were. Dan Brown's an expert at this; the Da Vinci Code is a wonderful read, but his "Fact" disclaimer at the beginning was dreadfully irresponsible of him, especially considering how many errors riddle that book (not even counting all of the ones dealing with Christianity...that's a whole different subject).
The moral (this coming from someone trained in journalism in high school) is to be responsible when you blend fact and fiction together. Use disclaimers, provide an author's note at the end of the book. Story is king, but if you knowingly have to twist something, be sure to let the readers know about it.