Recently, my mom found three glaring errors in the first page of a novel she was reading. The first scene in the book was at a beach we've visited a number of times, and the author obviously hadn't because most of her physical details were completely wrong.
I've spotted innumerable place mistakes in books, as well. Civil War slaves hid in kudzu that wouldn't be introduced to America until the Twentieth Century, locals in the North Carolina mountains were called crackers, trees bloomed in the wrong month, and so forth.
Errors like this make me paranoid about setting my books in places I've never been, and I research like crazy to make certain I get it right. I also try to get someone familiar with the territory to read through my descriptions.
Even worse than errors, however, is the danger of being patronizing. I've read novels where the author's contempt for an area was obvious in the stereotypes and misinformation. In other words, don't write about rural Georgia if all you know about the area is a few episodes of THE DUKES OF HAZARD you held your nose through.
If you're not willing to get it right, set your novel where you know.
REMINDER: August 1st is the final day to register for my “The Big Question: How to Create a Powerful Novel from a Few Ideas and One Big Question" workshop. To learn more go to