Interview Statistics and Acceptance Rates

It varies pretty wildly, depending on how the school treats interviews.

From my own research, there are basically three kinds of schools--those that have applicant-initiated interviews (Tepper, Duke), those that use the interview as "just another data point" and therefore invite a higher number of applicants (Wharton), and those that use the interview as a sort of "final hurdle" (HBS, MIT, Haas).

Just from my research, it generally fell like this:

HBS: Interviews around 25% and accepts around 50-60% of those interviewed
MIT: Pretty much the same as HBS
Wharton: Interviews around 50% and accepts around 35% of those interviewed
Haas: Interviews around 25%-ish, and accepts around 65-75% (they have a slightly higher acceptance rate than most schools because of Super Saturday--a higher majority of students who go to SS are accepted because attending SS is considered a strong sign of interest, and therefore likely to help the yield stat).

Duke and Tepper allow candidates to sign themselves up for interviews up to a certain date, and then after that are invite only, so there aren't many useful stats there.

If you check each school's thread on the BW forum, there's usually a discussion of these stats right around the time interviews are going out. I know there was for round 1, at least, for all the schools I apped to.