I've been buying stuff at Amazon, literally, since there was an Amazon. One of the creepy things about the experience to me is their "personal recommendation" algorithm is amazingly accurate -- they consistently recommend to me books I already own or have already read, and music I already own, but most of it things I haven't bought at Amazon. This wouldn't be so creepy, except that many of the books they end up recommending are in genres I've never bought or browsed at Amazon -- IE, there must be some kind of "type" out there that reads mystery books, classic literature, listens to classical, New Age, R&B, classic pop, and jazz music, who also has an interest in some of the more arcane subjects I do, subjects that are entirely different from the sort of literary tastes you'd expect from the things Amazon should know about me based on my behavior with them.
What's really interesting to me is that the other day I did a search for Space Food Sticks (a childhood thing), ended up at Amazon, and now their suggestions, which used to be all books I'd already read and music I already owned, are dominated by a bunch of survivalist stuff -- freeze dried and canned foods, tents, matches, and the like. Now, how many survivalist types read John Grisham, Michael Connelly, George Orwell, listen to Beethoven and Basie, Marvin Gaye, Aretha Franklin, and Doris Day? I assume there really is such a type, based on the accuracy of their recommendations in the past.