I'd imagine that the interviews are generally relaxed (though, not in a completely informal way), and are meant for you to get a sense of what the department is looking for at the same time that they are seeing if you seem like you'd fit in their dept. well. I had two interviews last year and in both I was asked briefly about my writing sample (why I chose the topic, if it was a specific issue that I wanted to pursue further, etc.) and about the broader philosophical questions/issues I was curre