I submitted my CV through the Google career website and about 6 weeks later I got an email with additional questions about my experience, my motivation and my availability for a phone interview. They scheduled a phone interview about 10 days later and send my lots of info on what to expect from the interview and they also sent a case which I had to prepare beforehand. In addition to preparing the case, I prepared extremely well by screening the entire internet for possible Google interview questions and I also informed myself a lot about Google AdWords, since I didn't know that much about it. The phone interview itself is very similar to the questions you will find online, notwithstanding that the interview is not that easy. During the case (that you get beforehand), the interviewee will play a stubborn customer and you will have to convince him/her to keep using AdWords. Currently I'm waiting for feedback on my phone interview.

Sent in application, no Cover Letter included. Had phone screen 2 weeks later. Very tough, had to prepare a case in which the interviewer said the first minute to scrap. Instead, he made a new one up and I had to improvise. Heard about this before, but hopped not to have to experience it first hand... Went horrible (I thought) and I felt very stressed and rushed as he was pushing me quite intense. Thought I would not proceed. Heard back 3 weeks later, I proceeded to onsite interviews. They flew me there, paid for cab, food, flights, everything. Very nice office and interviewers, felt great and had a good feeling walking away. Got a call back 1,5 weeks later, did not proceed due to lack of understanding of AdWords, which I think I understood well enough. Probably was some other reason, like structure of information or communication skills was not good enough. Anyways, a very pleasant interview process, a lot of help and support from HR how to prepare.