The data reveals the number of co-workers that join you Thursdays after work for a beer, and roughly where you all go. It knows where these same co-workers call home, and just exactly what kind of neighborhood they come from (e.g., average income, average home price) ... information certainly useful to attentive direct marketing folks.
As with most technologies there some good as well as bad aspects to it. For example, just today, we have a story about authorities locating a murder suspect with a lead from his cell phone. On the other hand, most of us aren't wanted for murder, but the data is being collected anyway.
Is your cell phone, an Orwellian "Big Brother," a helpful "Big Brother," or a "Big Brother" reality show view into your life?