There were a lot of stages to the interview process and a seemingly endless number of hoops to go through - phone interviews, online tests, proctored exams, even personality tests. After all that, I was offered an all expense paid trip out to their headquarters for an on-site interview. The night before when they took several of us interviewees out to dinner, I was told to "pretty much expect a job offer" because I'd made it that far.
The "interview" itself felt more like a college campus visit. Lots of tours and informational meetings herded around with other mostly fresh college grads, interspersed by a few short interviews. It seemed to go well, I thought. I remember feeling pretty positive about the nuts and bolts (what I knew, and the practice scenarios), but I was unsure how well I'd fit into their office culture. A week or so later they left me a no-explanations voice-mail that they were going to go with other candidates.
It's a big company composed mostly of extroverted young people. Lots of quirky architecture, clubs, and campus events. I've realized I really wouldn't have fit in well and being around so many highly-social people would probably drained me - I'm an introvert who'd rather spend my lunch break eating in my cubical with a book than in a massive dining hall "networking". I'm guessing that was the biggest mark against me. I was shy, quiet, and not super-social. I really really wish they hadn't acted so thrilled about me before and during the interview though. I quit applying to other jobs because I'd been told they were pretty much a sure thing, then out of the blue they dropped me and I was left at square one. I'm kind of pissed they took up so much of my time when they probably could have realized I wasn't a good fit early on.
Main advice to other applicants: Keep your guard up even though they're acting all nice. With a company so big, it costs them nothing to run you through the process even if they choose to drop you for someone else in the end.