Everything you read about the multi-stage hiring process is accurate. It begins with a phone screener with a recruiter. Then phone interviews or Google Hangouts with a variety of folks relevant to the job. Writing test. Later, on-site interviews, which are tough but fair. If you pass, your informational packet with all the notes and data from everyone who interviewed you is reviewed by a Hiring Committee which never meets you (to add a layer of objectivity). After that, if you pass, the packet moves on to the Executive Committee. It is profoundly important to prepare for every interview as if one is defending a PhD thesis, only the thesis is you, the candidate. I prepared for several weeks, brainstorming potential questions, researching the company and the role and thinking how I would answer the questions. I tried to sleep well and eat well. Even then, despite all the preparation, I left the interviews wishing I had done more. Everyone at Google is really smart and very good at his or her job. Those who interviewed me were no exception. They managed to ask me questions that really challenged me. I left the interview feeling I hadn't answered those well and didn't expect to get a job offer.
I was kept informed at each stage by a great recruiter where I stood and whether I was going to the next stage and what to expect. The whole process was incredibly professional and rigorous.