I did mine this past week at UTSW in Dallas. It was very easy and conversatoinal. But he also interviews for UTSW and he spent at least 10 min. playing up his school as a much cheaper and equal option (I interviewed there). Plus he did residency at UCSF, where I've interviewed, and he compared that to the others as well. Overall, he seemed to give me advice as a peer rather that trying to test if he wanted me to go to Duke. As to what that says about my admissions chances, who knows....
It seemed kind of weird not seeing the Duke campus or the adcom staff. I didn't recieve a packet or anything either. But I am getting very familiar with UTSW campus; I've had 3 interviews there-those two schools plus navy hpsp.