I started off getting a phone call from the recruiter for this position who initially made sure that I understood AppNexus's business model. Then we had a 15-20 minute conversation about what I've done, what I like to do, and the role itself. After a nice conversation, she invited me to come in to meet the rest of the team. Soon after, I got an email from the recruiting coordination team setting the interview up.
When I first came for my interview, I was showed around the office by a member of the coordination team. He did his best to make me feel comfortable by introducing me to people in the office, getting me a drink, showing me the bathroom, etc. We then sat down and had an informal conversation about what I've done, what I like to do, etc. Pretty boilerplate.
Then the tiring part started. I met with ~6-7 people over the course of the 6 hour interview. Al kinds of questions were asked, from workflow, to conflict resolution, to hypothetical problem solving. It was a REALLY intense interview and although I felt I was doing well, I had no idea...all of the interviewers were very friendly, but I took that as them being polite, not an indication of approval.
After the marathon interview session, I was told I'd get a decision within a few days. A few days later, they said they wanted me to come BACK. I was going to be out of town, and was a bit frustrated by this. Instead of coming back, we had a Skype session where I spoke with a few members of the team again and just went over some basics. I was glad that they were up front with the concerns the had about me; it was completely transparent, which alleviated the frustration I had about interviewing again, after such a long initial interview.