SRE applicants have rated the interview process at Google with 4 out of 5 (where 5 is the highest level of difficulty) and assessed their interview experience as 100% positive. To compare, the company-average is 66.4% positive. This is according to Glassdoor user ratings.
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The process took 2 weeks. I interviewed at Google (San Francisco, CA) in Mar 2010
Interview
Contacted by a recruiter on the phone, passed a few idiot proof screening questions, then was scheduled for an on-site interview consisting in 5 interviews, ranging from theory to coding on the white board.
Overall experience was OK, one interviewer wasn't really cool, the other folks were great. I have been pretty disappointed by the way the recruiters act (e.g: don't give you any response, you need to contact them to have feedback).