One should be careful to not go public about this intent (to game it). Someone had dedicated blog about his studies, preparations for BigG interview, he was reject right away without even a phone call... This story was on HN.
When I say game, I mean: practice questions you can expect to get (a little googling will help).
To think anyone would get through those interviews without prepping is ridiculous. Google specifically actually tells you to prep and what things to practice.
And also, since so many people do prep, the bar for acceptable performance is much higher than it would otherwise.
At this point, I'm not sure what these interviews are supposed to be measuring.
I guess the level of dedication/passion of how much one wants to get a job there... That's seems the only "reasonable" explanation so far :)
Actually making it through an interview and getting an offer is much less common, for (what I'd consider) obvious reasons.
I interviewed at Google without any preparation and was not given an offer. I would have liked to have the time to prep, but I didn't, and I assumed I would not get an offer. I didn't do horribly, and I was encouraged to prep and return. I believe I'm good enough that if I prepped I'd get an offer--I simply don't have the time to jump through those particular hoops at this time, for better or worse.