In September 2009, a Google employee, Marie, announced via the Google Docs forum that published Google Docs (which are made public by default) would be crawled, indexed, and used to serve SERPs:
This is a very exciting change as your published docs linked to from public websites will reach a much wider audience of people.
In other words, Google Docs wanted to flip its users’ data public to make more money out of it Facebook-style. In July 2009, two months before the announcement that linked-to published docs would be indexed, the Google Docs team removed a feature that automatically tagged published documents as “published”, making it really hard for users to keep track of which documents were potentially indexable. Technically, only docs linked to from a Website were crawlable and indexable, but as one commenter on the forum put it:
If someone who knows the URL for my published document, they can link to it from their own publicly crawled webpage, thwarting my attempts to avoid having it crawled. That means that I’m at the mercy of anyone who gets their hands on the URL for my published Doc.
Today, Google did not apply what Marie said it would. If you search for “pdf site:docs.google.com” on Google, no documents are found. If you do the same query on Bing, some 1.500.000 documents are found. How come?
Even after you publish your documents, spreadsheets or presentations, they won’t appear in the Google search index; however, other search engines may potentially index published docs.(from Google Docs Forum)
Google probably did that to avoid a PR mess around a central product of its recently-launched Pro Suite. Even if indexing was a good idea, strategically, it was too easy for the competition to hurt the image of Google Docs by arguing that Google could leak out to the world your sensitive business information. Nevertheless, instead of giving up the fight, Google decided to shut the competition down by allowing them to crawl and index Google Docs’ library of published docs. In the case of MSFT/Bing for example, Google is giving away a priceless source of information to Bing users, making Bing a more attractive search engine. On the other end, Bing users get to discover and get used to the universe of Google Docs. Google traded a bit of its search pie for a bit of Microsoft’s Office pie. Interesting!