My pet peeve - when authors don't know how to use the words "then or than", "prostate or prostrate", or mixing up "to, too, two" words. I think they stopped teaching grammar and spelling in about 1970. Too many people rely on spell checkers! If you're (not your) not sure of your grammar, use http://www.grammarly.com/?q=grammar&gclid=CICe_f3n1K0CFeYBQAodnyvElA