Quite messy interview process.
First of all, I have the sense google only works trough refers - if you have one, you will go, otherwise you will not. This actually is quite a problem, because if you are referred what happens next is that you got interviewed almost 100%, but then you are cut off because of lack of experience later on, thus meaning you lose time.
I got contacted from an HR quite sometimes after I got referred, and passed the first screening, with very basic questions.
I then had a phone interview with a Googler who was quite hostile to me and made me just a couple of questions. Google is super structured - they really want you to be almost like a robot.
Got a mail one week after saying I did not pass with no explanations.
I personally think it is impossible to prepare for Google. Googleyness was not tested to me (and how to, in case? it is not even clear what it is), questions on Google products were not tested either, just one behavioural questions after another, with no real true answer (also; the interviewer test one question after another imo reading a paper, thus not adjusting to what you say/don't say). The sense of indefiniteness I had in the whole process, the total absence of reliable metrics on which I was judged on and the absence of a true feedback left me very perplexed, and I do not think I will apply to Google again.