I am an Adcomm and my advice is to call them by their first name at your own peril. Always address a professor by Dr. X or Professor X unless they give you permission to do otherwise.
A recent example. I was copied on a response to an email where the applicant began Hello "Jim" and "Bob." I am a prospective applicant and am interested in meeting with you on Friday .... Jim and Bob! I asked "Jim" if he knew her and he did not. He didn't care for her overly casual greeting, either. I know I didn't care for it. "Jim" and "Bob" are not just ordinary professors at my institution, they are famous and important people (in more than just the department, they are world renown in their field and by lay people who track this field, i.e. they give autographs to people).
Her application is tainted by her casual references....and not in a good way.
