If the rulings are fair, I'll go along w/ the DM's rulings even if I don't like them. However, if it appears that there are questionable rulings where one player is consistently favored over another, I will object (strenuously). Or when my natural 20 on an attack roll is ruled a miss (against a normal skeleton while using a quarterstaff).
I wish my DM would actually start implementing some of the rules. I have never had him tell any of us that we could make an attack of opportunity, for example.