The interview process lasts a few hours on-site at HQ. Check-in earlier by at least 10 minutes because you'll get more of a chance to make a good impression with the receptionist. This is important because no one person decides if you're hired - it's a panel decision and everyone's opinion counts. Being culturally relevant is very important here and this is made clear by one of the interviewers checking for "cultural fit." Some may think this is unnecessary, but I felt that it was extremely useful for both the employer and potential employee. Although everyone is measuring your cultural fit, there are also technical interviews where you get to explain and showcase the extent of your knowledge and applications you have experience with.
After about 4 interviews with 4 different people, you'll be taken to lunch while they discuss all about you and decide if you should stay for round 2 of interviews or be sent home. The least you'll get out of this is the opportunity to learn about a new company and a free lunch!
At the end, you'll face a long technical question...see below.