The interview process was fairly exhaustive, where I had seven interviews/sessions ranging from the hiring manager to HR, the lead designer, CTO, CEO, etc. The final step in the process was a whiteboarding session in front of a group of stakeholders including the hiring manager. I have done my fair share of whiteboarding/cases, and what I've learned is that the amount of experience the hiring manager has in administering these exercises is *very* important. In this case, I could tell that the hiring manager had given many of these challenges in the past, as there was the optimal amount of guidance (guidance without detracting from the rigor and difficulty of the exercise).
In general, I felt that the questions asked during all of my interviews were fair and did a good job of gauging if I was suitable for the position. The HR person coordinating the interviews got back to me quickly, and the process moved along at a pace that gave me enough time to prepare for the next interview without leaving me hanging.