Phone interview briefly covered my background, followed by a healthy mix of advanced software engineering and C++ questions. Touched on concurrency, multi-threading, object oriented programming, memory leaks.
On-site interview consisted of multiple engineers coming in for about 20 minutes each, one or two at a time. Some would simply ask me about my background and get to know me as a person, and explain their roll in the company and the type of challenges they faced daily. Others would present technical problems that required working on a whiteboard. One question was designing the back-end class hierarchy for a product marketplace website. The on-site concluded with a rather informal lunch with a senior manager to discuss about where the company was at right now and where they felt you would best fit in.
Technical questions were not extremely difficult, so long as you had a solid grasp of advanced programming techniques and practices.