Here’s a thought. With the rise of AJAX applications this is bound to happen, and may very well have been implemented somewhere, even though a quick search didn’t reveal a lot. So here goes:
By adding a few clever Javascript events to a web page, it is possible to track user behavior on web pages far more than with the typical methods.
Similar methods have for a long time been used on some sites (including my own Spurl.net) to track clicks on links. A very simple script could also log how far down a page a user scrolls, over which elements he hovers the mouse and even infer how long he spends looking at different parts of the page and probably several other things usability experts and web publishers would kill (or at least seriously injure) to learn.
Even though it’s nowhere near as precise as the famous eyetracking heatmaps (here’s the one for Google’s result pages), it provides a cheap method for web publishers to help better position ads and user interface elements, experiment with different layouts, etc.
Does anybody know of implementations like this? Does it raise some new privacy concerns?
P.S.: I just saw that Jep Castelein of Backbase posted some related thoughts this summer.
hjalli.com - Hjálmar Gíslason 
Start a web service. Ad networks and webmasters would pay for this.
Boy, and we thought cookies were intrusive!
People were up in arms over gmail scanning mail for ads (of course, mail has been scanned for ads/viruses for ages); were wary of Tivo collecting usage data and many have boycotted Amazon for recording every click, view and purchase of its customers.
Of course new privacy concerns will be raised, it would realize some of the worst nightmares of internet privacy watchdogs.
Developers would eat this technology up without hesitation. The majority of the Internet public, not renowned for knowing the intricacies of what’s really going on, wouldn’t know the difference. A handful of people would make a big fuss. Eventually, people would get used to it–it’s just a bigger, better cookie.
Great points, Allen.
I am looking at this from an advertising guy’s perspective. I’d love to know what people are paying attention to.
Peter: I’ll leave this to somebody else, very hard to create any competitve advantage on this and the Urchins of the world will soon have this as standard bits.
Allen: Good points. I agree that this will probably face some loud critic from the privacy concerned minority, but there is no way to stop this really.