In other words, Google will pay you (and make you famous and possibly hire you) to find their security bugs for them.
Rocking.
Sadly I don't know where I would start on a project like that. Maybe some googling will give me some ideas. (ahaha irony)
EDIT: after reading parts of the Hall of Fame for people who've won the money, I'm less convinced that I can make an immediate contribution, but more convinced that I want to.