2 things to consider. Google can't do half of what the Federal Government could do with your information. You should be more worried about the government. Also, if the government does spy on you like you're fearing Google could do, there's nothing you can do. They're already in office and they know you can't stop them. Google on the other hand, would have to tread pretty lightly because if they blew the trust of their consumers, they'd be out of business in no time. They have a higher risk involved than what the reward would be.
I'm sure they know a LOT about us, but I doubt they'd ever try to use it maliciously or be secretive about it. And i'm sure someone will post a link to some conspiracy theory or whatever that "disproves" what I just said, but I don't believe they would. They may not jump at the opportunity to tell us what they use our info for, but we make that choice when we purchase and use their services. Unfortunately the same happens when uneducated Americans go place their votes based on feelings and handouts instead of actual research and knowledge, and then they ruin it for the rest of us.