If there's anything I learned this application cycle, you need to SELL yourself. All of the interviews so far seem like they are conversational and relaxed- that doesn't mean you should just chill and talk about whatever the interviewer asks you. You need to guide the conversation to touch on the important points you want to make without appearing to dominate the conversation.
We've interviewed at both Penn State and Case Western - so this will be relevant to you...
I interviewed at Penn State first. It was my first real, relaxed conversation and in retrospect, I realize that I didn't sell myself as well as I could. I was mostly relaxing and responding to the interviewer's questions, which is part of what you are supposed to do, but I didn't go out of my way to tell them about how I would be a good match for their school. For whatever reason, I didn't do this and I think that was mainly responsible for my post-interview hold.
Then, a month and half later I got an interview at Case Western. During this time between interviews, I realized that I needed to do a better job of selling myself. Perhaps Case just made it a lot easier because I happen to be a great fit - but I made sure to touch on the particular points I wanted to make, and I felt I did a great job doing so. Even within the framework of the typical questions such as, why medicine, tell me about your research, why Case Western, I was able to continue to sell myself. And that's what its really all about. End result, acceptance.
This is coming from a guy with a slightly-above B+ GPA. So clearly, it's not my GPA that's selling me - if I'm relying on that, I'll be SOL. You have to give them other things to focus on.