I've heard really great things about ZS and its culture from a friend who works there. I was referred and had an hour long phone interview, after which I was invited for a full-day in person interview. I had one behavioral interview with a Principal, two technical interviews and one sit-down with a current employee to see what they do - note that the sit-down is actually an interview to see how interested you are in their work! I felt that I did really well in all but the behavioral. I had bronchitis the week before the interview and was still a little hoarse (should have requested a change of date!) and the Principal that I interviewed with got really testy when I coughed a few times and had to drink some water. After a while, he just tuned out and started looking at his computer. I think it was unbelievably rude and unfair of him to dismiss me for a cough, but I really should have told them during scheduling that I needed extra time to recoup and lose my cough.