Hey, OP here. Thanks for the mention of Xprivacy - I wasn't aware of it. :)
Like everyone else, I'm always learning. Just sharing this post for others who weren't aware of Amazon's business model here (which does seem somewhat hidden).
Amazon aren't being particularly underhand here; a tiny bit of googling will explain how Underground relies on app usage tracking (not location tracking).
I agree that "Joe Average" may not question the free lunch, and that's a problem, but it's exactly the same problem as existing free apps like Gmail, Facebook, etc.
If you're a technical person with an interest in privacy issues, you need to pay a bit more attention.
Interesting. I've been thinking about this recently and, yes, while I can sit in front of a computer screen for eight hours, I reckon I'm only productive for six hours. So I try and work in three 2-hour bursts.
It's worth saying that my situation's slightly different in that I work for a tech company, but I'm not a coder.
Indeed, I could have gone into more detail but people don't tend to read long posts. So I could have talked about the time I was in a taxi in Spain (not speaking the language) and my only directions to a conference venue got corrupted, or the time when a note to myself about my doctoral thesis disappeared, or...
Like everyone else, I'm always learning. Just sharing this post for others who weren't aware of Amazon's business model here (which does seem somewhat hidden).