Chris Sacca (former Google employee) is an extremely well connected venture capitalist in the Silicon Valley (even though he now lives some 4+ hours away in Truckee).
He is featured on a somewhat recent episode of TWiST. Check it out at, https://www.youtube.com/watch?v=SK4ezQrTqFw. He offers some really interesting insight into marketing trends (both past and present) and how social media sites are using your data. In the interview, he mentions a company called, Path Intelligence (http://www.pathintelligence.com/) that actually is tracking cell phone movement. It is all anonymous though, so they aren't tracking you specifically, but still a little creepy. Overall he leaves one with the impression that everything is on the up and up.
I wouldn't overthink things, but it's also never a bad idea to error on the side of caution.