Back when the First Reader was publishing regularly, he used to run his papers through a spell checker because he knew he couldn't spell. Initially he trusted this step to clean everything up. After a certain amount of mostly civil discussion about how using "they're is" for "there is" affected the credibility of his work, he started getting me to skim everything as a second check.
I've been reading a lot of indie sf/fantasy lately - books that the authors have released directly to Kindle without going through a traditional publisher - and I am becoming grouchy about the plethora of minor errors that are probably due to an over-reliance on spell checkers. A number of indie authors brush off criticisms of this sort of thing by saying, "Oh, everybody is down on indies for having too many typos when actually we're no worse than trad publishers!"
That is: I don't care whether Indie Book X has more typos than Trad Book Y. What I care about is that Indie Book X had enough careless errors sprinkled through it to yank me out of the story on a regular basis. And the type of error was almost always a case of a legitimate word used incorrectly to replace the "right" word. And it's not just discreet/discrete or deserts/desserts, which three-quarters of the English-speaking world predictably gets wrong. It's happening with common words that I can't believe any marginally literate person would mix up.
"Her eyes shown with delight."
"Never mind the passed, let's talk about the future!"
"I have a grate idea."
"There's a general disquiet among the populous."
"I'm go to practice more next time."
I just don't believe that anybody who writes a pretty decent 80,000 word book is really confused about how to spell shone, past, great, populace, or, for heaven's sake, going. Okay, I might give them a pass on populace, but even if they're shaky on the correct spelling they should realize that populous isn't the word they're fumbling for. It isn't even the same part of speech!
What this looks like to me is that somebody ran a manuscript through a spell checker and didn't bother to read it afterwards. Because they believed all their problems had been solved? Or because they believe some of the cockamamie advice I've seen handed out, like,
"Don't worry about grammar, spelling, or typos. That's mere craft; you need to concentrate on inspiration."
Or the much-repeated assertion that "If a manuscript is perfect, you probably edited it sixteen times and squeezed all the life out of it."
Kicking the reader out of a story trance and into musings about what you probably meant to write is just not a good idea. I don't care if you got "just one little letter" wrong. (There's only one letter's difference between shone and shown) Relying on spell check to fix all your problems is lazy, and it turns nice, calm, easygoing readers like me into crabby ranting maniacs. DON'T DO IT.
(Here endeth the rant.)