Whoa. I just read through this thread and I have to jump back a couple of pages:
I find it INCREDIBLY annoying when I find egregious misspellings in a published book. Confusing their/there and then/than in particular annoy me, and I'll tell you why:
I don't move my lips when I read.
What I mean by this is that, unlike some, I don't "sound out" what I read and then interpret the sounds. I just read. And I am a voracious and lightning-fast reader. When I run into a sentence that uses "then" when it should be "than" I actually mentally trip up a bit and have to waste 3 seconds of my life re-reading the sentence and trying to puzzle out what the cretin who wrote it is trying to say. I have actually abandoned books that make this mistake consistently. It is simply too painful to go on reading them, and I will gleefully thrash them on my Amazon reader reviews. Thus I disagree with George when he claims that "If you can undrestnad waht the syombls maen tehn the msseage is succsseful." Does that mean that as long as my patients survive then I'm successful, no matter what other complication they have? Obviously not.
If you are WRITING A BOOK then you are a PROFESSIONAL WRITER and should WRITE WELL. Actually, to be fair this is the editor's job, but I'll hold authors accountable to some extent, too. (Obviously this does not apply to forum posts- just published works. And, actually, I'm more lenient with fringe self-published stuff, too.) I agree that spell-checkers are a crutch and that editors who rely upon them should be flogged. It also doesn't help when the spell-checker tries to "help" by automatically changing a word that I spelled correctly into the wrong word. That really chaps me because it makes ME look like an idiot, and since I have a love of obscure words and complex sentence structure it happens to me quite a lot.