The process took 1 day. I interviewed at Sphere Institute (Burlingame, CA) in May 2011
Interview
First you do an hour long "logic" test. It kind of reminded me of the kind of logic/math problems you would see in a MENSA puzzle book, but none of them were really that difficult. Then I was interviewed by a few different people, sometimes by two people at once, sometimes it was a 1 on 1 interview.
Interview questions [1]
Question 1
Tell us about a project you worked on and what you personally contributed to make the project better.