Tornadoboy's source is good, but primarily focuses on the amount of heavy communication between Google and government, so I'd prefer to add this source specifically, on the strong revolving door effect:
Campaign for Accountability's page, above, has an interactive chart where you can see which employees, by name, moved between Google and the government during Obama's term, and what positions they held on each side. Beyond the "Read more" link is also a significant amount of specific detail about some of the more notable transitions.