It is a major pet peeve of mine when someone uses the wrong meaning of a word, kind of hard for me to explain. Like using 'hole' instead of 'whole', or 'where' instead of 'were'. Also run-on sentences. Most of the time if I see a post with run-on sentences, then I don't bother reading it at all. I understand some typos that happen because of fast typing, but when it's hard for you to understand what a person is saying, and when you have to go back and read the sentence again to actually be able to comprehend what they were typing, well it gets annoying. I am by no means a perfect speller, but I usually have dictionary.com open at the same time to check some more difficult words.