Ethics and paper writing

Here's one for discussion.
I'm taking an Information Systems class and we recently discussed ethics. With so many of us plugged in to the net, the exchange of information is quite fluid and that includes our personal information. A particular company called doubleclick.com tracks peoples patterns to better assess what products to market to them. I imagine an example would be if you go to a site for buying novels then they would let marketers of stores like Borders know that you are into books and to send you information and advertisements.
Do you think it is right for them to do this? What about other spyware that takes up space on your personal computer? How about personal information? People sell this info all the time and get away with it. Is anything private anymore?

On a side note...we also talked about plagiarism. I asked the professor this question based on a real situation that happened to a friend of mine who is a grad student. "If I write a paper for a previous class, and I am assigned a similar paper in another class is it plagiarism for me to turn in the paper that I had previously submitted and received a grade for?" The professor went back and forth with the argument and eventually concluded no, it is not plagiarism. My friends professor said it was. Hmmm...