It seems to me that if you're a dev that wants to work at Google, sending them a cover letter and resume is a waste of time. Google can afford to pick almost anybody. You've got to stand out. I'd imagine that it's probably best to become an active contributor to an OSS project that has a lot of impact or create a startup that could potentially target Google's market and hope to be acquired. Obviously the startup route is much riskier, but more rewarding. Regardless, it seems that if you want to work at Google, you've got to make a name for yourself.