And just to add (since I typed that last bit from my phone on the train)...
This has been around for a while. It is picking up steam now of course because people are getting more advanced in their advertising. But at the end of the day this is what a lot of people on /. have asked for in the past...less irrelevant ads that bug the crap out of them. Well, you got your wish. These are targeted based on your actions and thus will be of more interest to you. The people who decide they don't want ads AT ALL have likely already blocked them in some manner, and thus should not be weighing in on this discussion to just gripe about something that no longer applies to them.
Also, for all you people who love receiving Amazon's emails with suggested products for you to buy--guess what? This is the display advertising equivalent. And I can't stress enough how easy this is to foil. Don't like? Block ads, or just wipe cookies when your browser closes as most of these systems are cookie-based in their tracking and the ones that use Flash zombie cookies are getting sued to hell in a handbasket now.