"Many companies have systems for tracking customer habits, but Amazon has collected info longer and used it more proactively. It now has technology that tracks data on those you buy gifts for, and it reserves the right to sell it all."

Good catch up article on Amazon and privacy issues about the data they collect. If you remember, around 2000, Amazon changed its privacy policy to allow them to sell your data without your consent (you can opt out, of course, and stop using their site). From Wired News.
URLs:

http://www.wired.com/news/ebiz/0,1272,67034,00.html