I agree that clicks will move away from Google and onto Facebook amongst certain demographics. However, I hate the idea of comparing time spent on Google to time spent on Facebook. I would expect that Google wants you to spend as little time as possible within their search engine. Less time on google means better/perfect results faster.
More time spent interacting with a site means more opportunities for advertising (in all its forms), and that's what these companies live by. You don't think Google wishes they had a successful social product similar to Facebook?