Two phone interviews over 2 weeks - 1 per week. Could have gone faster, but I didn't want to take too much time off work. And followed by a day of on-site interviews.
Most of the questions were about problem solving, and a lot of the problems were about the problems the team has faced in the past, and so were about how to go about building scalable systems, or removing bottlenecks. Some algorithms / data structure / OO-design questions were mixed in as well.
Two non-technical interviews - one with the hiring manager over lunch, just getting a feel for each other, and one with the Amazon recruiter at the end of the day, talking about Amazon's compensation structure, and other benefits.