As a reader I have often picked up misspellings and grammar errors which have somehow slipped through, though as a writer I've often been guilty of those mistakes myself. I have a fantastic fiancée who reads every chapter of mine and finds the errors I've made. Most often, my errors are simply missing letters or double words (ie, double double words) as my brain just hasn't caught up to what my eyes see.
My pet peeve, and I have seen this in a novel or two, is "definate" instead of "definite". What was really amusing is that on one occasion, less than a paragraph earlier, they had "finite" correctly.
I also came across a word recently which I thought was a spelling mistake, but after finding a dictionary, I realise it was not, though there is still the possibility that the word choice was incorrect. The word was "complaisantly" which I thought should have been "complacently" having never come across the former word before.
for clarification, what is the difference, if any, between spelt and spelled?