I was referred by a friend for the project manager position. The HR contacted me and then arranged for the phone interview. The hiring manager called me and asked me to write down the answers on the google doc. After the phone interview, and I was given the onsite.
For the onsite interview, I met with 5 people, and lunch with the hiring manager. 3 out of 5 people interviewed me are from different groups, not from youtube. The hiring manager has no power on the hiring, but does seem to be a very nice person to talk to. First interview is with a program manager who asked about a lot of PM process questions. The 2nd person is a senior PM who asked about analytic questions. The 3rd person is a software engineer who ask technical questions and the 4th person is a manager working at the data center who ask more about daily operation questions.
My overall impression about interview at google is: people are very smart, and they are very proud of being the best, and in some way you might call it arrogant. If you want to be part of those smart geeks, I guess you have to act the same way as well, since this is the culture. To get an offer from google, you are not only have to be well prepared, and ready for any strange analytic questions they are going to throw at you, and also treat it like a lottery: if you met nice people, your chances are much higher, and when you met with people who are just want to show off their IQs, or simply just want to learn some new ideas on what they are doing, then you either have to prove you are much better than they think you are, or you just accept the fact that today is not your lucky day.