Yes, I had the second interview this last week... It's nothing too high pressure. The woman is nice so it was an (in my opinion) easier conversation (I always felt stupid during my first interview). The interview is not too difficult, just know your goals, your resume, and why CMU. There is no "ethics" question or many behaviorals. It's pretty much "walk me through your resume, how are you a good candidate, tell me about your background in CS, Math, Stats, etc."
My impression is that this interview means that they think we're a strong candidate, so they don't want to reject us. They're giving us another opportunity to prove ourselves as being able to interview well (and have good placement) because we didn't do well on the first interview. That's also a confidence booster going into the interview.
I think the interview went generally as well for me, so now I'm just crossing my fingers until the 8th.
Anyway, good luck and kick some ass!