Grades - more properly good grades, oustanding grades are like giving yourself options. They will open doors at places where no one knows you and you give you the chance to be known. You don't have to always have the greatest grades for competitive specialties if you're willing to put in time personally with those folks. For instance, you have average grades but want ortho, well one way to help yourself is spend all waking time with your ortho folks at your school as well as being aggressive about outside electives at middle tier programs who will give a guy a shot because they like him (many top tier prorams and I mean top tier programs across the board of scpecialties - are elitist and snobbish - and tend to take only their elitist and snobbish counterparts from medical school). Also research, especially if you get published, if great to make up for lack of 10% grades.