I've caught two silly mistakes, quite often repeated, as far as spelling choice. Reign and rein, for instance -- I'm dealing with nobles, so both words get used in Uncertain Heirs, but I noticed my common mistake: "The chauffeur
My other weird, yet consistent mistake, was writing lead in place of past tense led every. Single. Time. I know the difference, I really do, but for some reason I wrote it wrong -- but I did it consistently, which fascinates me beyond measure.
This, folks, is the perfect reason for why you should take three to four weeks rest in-between drafts. Fresh eyes catch the silly mistakes, and save you from the "OMG! I should have caught this" embarrassment of having others read it and catch it for you.