Nothing clear-cut, sorry. Although their policy does say they permanently log all requested domains.

Anecdotally, i run a private community site on "foo".dyndns.org with no inbound links anywhere, never submitted to google webmaster tools, but it shows up in a google search for "foo". Google public DNS is widely used amongst community members.

I haven't seen any links but I wouldn't be surprised. It was a theme (meme?) at Google to create a free service to generate data for other stuff. They create their 411 service to collect voice recognition information (for example). And I do believe Ingress (game) was originally a way to augment their maps data.