My interview was fairly non-standard, since my interviewer had specifically requested me (we met on a project during my internship last year, and he was impressed with how well I worked for an underclassman university student.). I was presented with an actual problem that the group was planning on having me work on, and was asked about how I would approach the problem. It was very imformal, and very relaxed, with us just sitting in a small conference room and working through the problem.