Grades are important (class rank, boards) as well as letter of rec., and personal statements (I was surprised that most of the programs had thoroughly read my PS, and had things highlighted). You must meet a basic standard academically to get an interview. So if you get one, they at least know that you are qualified academically to make it through the program. Interviews are opportunities for programs and yourself to get to know each other better. A great candidate on paper may seem a poor fit for certain programs after an interview, and vice versa. You have to have a decent personality to match the program...your going to be with the program for at least 5 years...so you don't want a stiff bookworm as part of your team. A smart and personable applicant is probably ideal, using whatever the standards are at each program.
