No, the worst thing that Google,[1] can do is share that information with credit card companies, HR departments, health insurance companies, etc, who do have the power to ruin your life and are much more likely to do it than the government.
What happens when the advertising money hits the wall and can't support revenue growth sufficient to keep the Wall Street analysts happy? At some point some MBA is going to figure out that HR departments would love to be notified about e.g. their employees joining say a cancer support page. It sounds inconceivable today, but I bet people who started using credit cards in the 1960's and 1970's never expected that one day the various credit organizations would band together and sell your information to literally everyone, so that you could be denied a job because of your credit history.
I think it's important to keep some perspective, and I feel like people on HN aren't doing that here when they direct all their blame to the government over this issue and hold Google, Facebook, etc, who created this surveillance apparatus, blameless. Corporate America is much more likely to screw you over than the government. They have a profit motive to do so, and can get away with screwing you over on a mass scale in a way the government cannot. I don't know a single person who has been screwed over by the government. I do know people who have been screwed over by credit ratings agencies, having job offers revoked because they struggled financially in college.
Maybe it's not inevitable or even very likely that Google and Facebook will sell your information to the highest bidder. But it's a failure of imagination not to pretend that it isn't possible, and if we're going to engage in slippery slope reasoning with respect to the NSA, let's be intellectually honest and admit that we've built a vast surveillance apparatus in both the public and the private sector, and there are numerous entities within both sectors who have the ability and perhaps the motive to use that information to hurt you.
[1] Or Facebook or whatever. It doesn't matter. One day these companies will become mature and will be headed by some MBA who has never written a line of code...