Hey! Sorry I noticed your post now, hope I am not too late.
I have had two skype interviews so far. One was pretty friendly and laid back, the prof asked me my motivation for pursuing research and what I enjoy the most. He did most of the talking, explaining about their program and stuff like that, it lasted for about 20 minutes.(I got accepted 2 weeks later)
I had another one, incidentally with Baylor and I have no idea what to make of it. He asked me my motivation again, other schools which I applied to, whether I have any other offers and then started grilling me about my research projects.
I have 3+ years of research experience and he asked me to describe the 2 major projs I was involved in. He challenged almost every thing I spoke of, the design of our study, the methodology, our results. He was not rude or anything, he wanted to test my knowledge by pushing my limits and just directed me into thinking about them with a different approach.
The discussion of my first proj ran a little longer than expected and he spent relatively little time on my second project.
Over all, I felt it was a very interesting discussion. At some points, I felt his qns were a little intimidating, but maybe that was my nervousness.
He closed the interview saying he enjoyed speaking to me and I will be contacted by two more faculty members for interviews soon.
It lasted for about 45-50 minutes.
I hope this helps and did you have yours yet? I also found a thread you can follow