I'll PM you later tonight (don't want to leave specific details here in case it comes back to bite me). I will say though that I have enjoyed the majority of my graduate experience at Carleton, and depending on what you want to do later on in your career, it can be a great school to gain practical experience at, as well as research experience. Congrats on the Carleton acceptance!
It seems to vary form school to school. I've only had two interviews so far: SFU and Saskatchewan. Both were phone interviews (SFU has an in-person interview day but I couldn't go because of work). In my interview for Saskatchewan I was asked a lot of questions about my research, mostly about my thesis project for undergrad (I had a fairly unique project, so they wanted to know more about it). They also asked me what unique quality I had that would make me stand out from other applicants, and what qualities I had that would make me a good clinican/researcher (standard interview stuff really, I had easy answers because I've been asked those same questions in job interviews before). And then questions like why you applied, why did you pick those researchers to work with, etc.
SFU had similar types of questions (it wasn't focused as much on my research as Saskatchewan). They also had a bunch of ethics scenario questions that I had to answer (these were scary). It didn't really feel the same as the Saskatchewan one did (the interviewer had the TV on in the background and it was distracting!), and it was my first interview so I felt really unprepared.
At the end of each interview, they gave me a chance to ask some questions, and then said that they would be in touch soon.