I'm just trying to say that one shouldn't expect their private files to be private when they keep them with Google. Many people however will have the opposite (and reasonable) expectation.

The least of anyone's concerns should be the actual ads that are displayed to them while using Google's services. It's what they're doing (or can do) with the data that concerns me personally. I don't know, or know of, anyone directly nor indirectly that doesn't have some information they keep private.