Originally Posted by Garrett

In a recent phone interview Dan Thies informed me that Google has been tracking click throughs on their search engine result pages (serps) for some time.

According to Dan, "when you view the source code of a Google search result page, you can see the format of the links looks like this: <a href=http://www.example.com onmousedown="return clk(3,this)">. That "onmousedown" event calls a Javascript function which tracks the click. In this example, it would be a click on the #3 result."

This javascript creates a little image instance that tells Google that, say, link #3 was clicked. Dan thinks clickthrough tracking may become a part of the algorithm.