I don't think the same engineers that work on products like some new app even have access to the kind of data that would come from that feature, nor does that sort of snooping even occur at google. It's not the NSA
That attitude seems naive. Google took a stab at replacing Wikipedia with Google Knol, Yelp (or was it Foursquare) with Google Places, and that's just two examples that spring to mind. It seems expected that Google would mine its own data for trends and look at how they could use that data to drive new app development or make existing third party apps irrelevant by rolling new features into Google Now, even if that data is mined only "in aggregate".
I would hope this to be correct, but I didn't see Google address it at all. A lack of transparency is a great way to foster FUD and a bad perception of what could be a great piece of tech. I get that they're building the marketing hype first, so hopefully it will be forthcoming.