Gathering data from your customers is very important. By understanding your customers needs and behaviours you can really service them well. That said, gathering data should ideally be done with the consent of the person.
Passive gathering of generic traffic patterns is done all the time on web sites, and fair enough. It is also useful to know how many of your emails have been opened and to track click-throughs. These are common, and as far as I am concerned proper practices.
There comes a point though when this is intrusive. Spyware is definately an area of concern, I am glad Bill Gates can draw some attention to the issue and attempt a technical solution but I am afraid the ethical companies that want to put a stop to these practices probably already have good codes of conduct, nothing will stop the spammers and scammers. Also we need to be careful to not ban ethical tracking and targetting just to try and make it difficult for the bad guys. Lest we forget the EU tried to ban cookies!