I did a mock interview with my boyfriend, which didn't help. However, if you can find someone who served on an adcom, or who genuinely has knowledge of the kinds of questions they ask-it would probably be worth it. I think DO interviews are not as stressful as MD interviews (having done both now), and the important thing is to look over your app, read the interview feedback on SDN, but to make sure you are friendly and not totally stiff.