You'll find a LOT of info on the web with tips about what to say or do in a grad school interview. These are the questions you should never, ever ask in an MBA interview.
So, how did I do? Don't come across as needy and desperate. Even if you felt like the interview went perfectly, the answer to this question will almost always be, "We'll let you know." Be confident at the start of the interview and at the end.
Is there anything else you want to ask me? If the interview is coming to a close and there is something about your application or personal background that you wanted to talk about but didn't get the chance, don't wait for them to ask you the right question. You can absolutely ask THEM a question in order to highlight a strong characteristic about your application.
Can your school find me a job? If you've done your research, you should already know where the alumni of each school are working, what their alumni network does, and what opportunities the school has for internships and summer employment.
What makes your program unique? You've already applied to the school, so you should know this. If you ask this question, it puts the interviewer in a defensive position. He or she may feel the need to "sell" you on the school, which will not be comfortable for them, and will not give them a good impression of you. Ask genuine questions about specific aspects of their program to show you've done your homework and are actually interested.
When will you let me know? They should tell you this at the end of the interview. If they don't, you can easily find out online when approximately the notifications are made. Connect with other MBA students online on message boards and Facebook. Most MBA interviewees ask this question. Be the exception.
How much money are your alumni making? Like the "Can your school find me a job?" question, questions about alumni in general can be off-putting. It paints you as someone solely concerned about making money and using the school for its connections. Not that money and connections aren't a big concern (after all, MBA programs are expensive!), but you want to seem far more interested in the school's curriculum and in how you would be a great asset there than on any monetary result.
Congrats on getting an interview -- rock it out!