A recent development in customer tracking actually collects information on people who may have never visited Amazon.com. Amazon's gift-giving recommendations collect data on the stuff you buy for other people. For instance, if you buy a toy train set in December and ship it to your nephew, Amazon knows you give gifts to a boy aged four to 10 who lives in Ohio and likes trains. Might your nephew enjoy the latest addition to that train series? Might he also have an interest in RC cars? Amazon will give you all sorts of ideas about what to get your nephew when the next holiday season rolls around.