I was mostly asked questions that try to determine whether I am a good fit to the Prof.'s research projects (~60-80%). Some questions about my abilities and my experiences. Finally, I was not told when I would know the result ...
I don't think telling you what kind of questions I was asked will help very much. The interviews are not carried out by representatives of Yale but by Professors, each of which probably has different notions of what a great graduate student is and most importantly have different projects.
Anyway, good luck on your interview and remember, if you were selected for an interview then the admission committee was most likely impressed by your application.
I hope that helps if you have more questions let me know