One summer evening at a Mariners game, I pointed out an error on the scoreboard display. I think it was a misplaced apostrophe or something. Mr. Fraser said something like, "Well spotted, Lady Pedantic." I replied, "That's Her Grace, the Duchess of Pedantry to you."
I know I can be a bit over-pedantic as a reader. I have no patience whatsoever for major historical errors--e.g. Europeans eating New World food in stories set well before they stumbled across the Americas. And don't get me started on the time I tried to read a baseball-themed book where the author evidently didn't understand how a starting rotation works.
I can be picky about much smaller things, too. I never name names, because I figure it's bad karma. Nobody is a perfect researcher. I'm sure I make my share of inadvertent mistakes, so I'm not going to sit around smugly pointing out those of others all over Twitter or Amazon reviews. But I've set aside many a book after 2 or 3 subtle errors in the first few pages because I've lost trust in the author and her story's world.
I'm not consistent, however. Recently I read two books that made horse errors. The first one was fairly subtle, but the equestrian world was a major part of the setting. The other was HUGE, but the horses' presence was incidental.
With the first book, I paused for a few seconds and thought, "Aw, man, she should've caught that." But the writing was strong overall, I liked the heroine, and I was so caught up in the plot there was no way I was going to stop reading just because she'd missed a small, breed-specific detail.
With the second, I was already annoyed with the hero for being melodramatic and self-absorbed and wondering how the author was going to stretch what to my eyes was a simplistic conflict out for another 40,000 words or so. So the horse error was the last straw, and I was glad to have a good excuse to stop reading.
Shorter Duchess of Pedantry: If you want me to finish your book, don't make errors of fact in the first few pages, before I'm properly hooked. Once you make me care what happens to your characters, I'll forgive you anything short of potatoes in ancient Rome or machine guns at Waterloo.