"On the heels of the big Apple love-in that is Macworld comes some interesting but alarming news. Recently a few blogs have started to indicate that iTunes is tracking your music preferences and using that data to recommend other songs from iTMS. The article provides a good overview, with some recommendations of its own. Basically, iTunes is tracking your music and sending the data back to Apple servers. This info is then used to advertise songs that may be to your tastes. A convenient feature, perhaps, but it raises concerns over privacy."
I wonder if Amazon's book recommendations fill them with fear too.