This is the first year Yale's history department is conducting interviews. This January, the Graduate School of Arts and Sciences mandated interviews for all top-level applicants in all departments before admission, in order to ensure people wouldn't drop the program two years into it. It has proven very controversial within the GSAS at Yale, and you can read more about it here: http://www.yaledailynews.com/news/2012/jan/11/grad-school-divided-over-interviews/
I had my Yale interview for history (modern German) yesterday, and depending on your interviewer, it could be a pretty rough experience (I personally had to attempt to avoid being backed into a corner several times). Good luck to all!