For me, it was the news (in 2005) that they were hiring JavaScript-specific engineers - JS was my true love, and though I didn't think I was anywhere near the CS-Genius stereotype I'd read about in the press, I felt I was pretty good at JS, so I applied on a whim, thinking that it was an outside chance, but the best I'd ever have.

By the end of the interviews, I felt I did well (considering that I'd read up on complexity theory for the first time the night before and had told an interviewer that I didn't know what a hashtable was), and felt that even if I didn't get the job, I'd had an awesome day, but still didn't really believe that it was really going to happen. Then it did. I think I worked out OK for Google (I'm still here 5 years later, at least).

My perspective was that of a foreigner in a land where CS was a path to becoming a suit-wearing enterprise software automaton - at the time, Google seemed like this romantic faraway wonderland, so the whole process was very removed from reality for me; the perspective of someone who went to a school like Stanford or Berkeley is probably very different and more realistic.