From talking to other employees, it sounds like the number and type of interviews varies depending on what team you're applying for. For me, I had a phone interview with human resources, followed by an in-person interview with a few of the people I'd be working with the most closely. In-person interviews tend to be pretty friendly and informal- they don't have a written-up list of questions or anything- and they usually give you a tour of the office and introduce you to some other people you'd be working with if you got the job.
The interviews also tend to be pretty intense. Interviewers will ask you to try to solve unexpected problems that they are currently trying to solve; they want to see what your problem-solving process is like. I would say my in-person interview was the most difficult interview I've ever had, and I left it (erroneously) thinking that I'd done poorly and wouldn't get a job offer.
