Hey there,
I interviewed there in January and I found the group format very relaxed. The interviewers were all very friendly and I didn't get any difficult questions. But I will say that a few of the students did get more difficult questions. I agree with the other post in that it is important that you go over your file before hand, they definitely ask questions very specific to your file. Also, I think it helps if you have a very interesting file. I got the feeling that if your file was very "normal", they ended up asking harder questions that didn't have anything to do with your file. For example, one student was asked what he would tell a patient who was just diagnosed with kidney failure and would have to go through dialysis.
One more thing, be careful when you answer any questions comparing MD vs. DO. One of my interviewers was an MD and when another student was trying to explain the difference between the two, he ended up in an awkward situation b/c he was speaking negatively about MD's. So don't say anything rash about how DO's are "better" than DO's becuase.....
Good luck!