Data mining with AJAX

Just had an idea: how about using Javascript to record client-side usage of your website?

The principle is this:

1. Register Javascript listeners which construct a list of events, particularly mouse, scroll and click events, along with the time that the event was fired.
2. Register an unload event which posts the information as XML with AJAX to a script on the server when the user leaves the page.
3. Browsing sessions can be collated on the server using cookies.
4. Create a player, which reads the events as XML and renders them using a DHTML 'cursor' and/or by firing events within the DOM. Could have a time slider and fast-forward controls, etc, depending on how complex you want to get.

Voila - see exactly what people are doing with your site. I have knocked up a test which implements the first two steps, for mousemove events, and that much works, so the whole concept would be workable. I can imagine it would break down if your site uses plugins (or Javascript navigation, depending on how easy it is to replay the events accurately) but that's a limitation you would have to live with.

There are obviously privacy concerns but this is relatively mild as no personal data would be recorded. Perhaps it could pop up a Javascript window.confirm() dialog asking if it's OK to record your behaviour. But it would be a very useful tool for examining site usage, especially for commercial sites. This is the way modern marketing works. I leave it up to your conscience as to whether it's ethical.