A number of individuals who have used third party Google AdSense click tracker tools, such as AdLogger, have reported that they are no longer working properly. In a WebmasterWorld thread, they suspect that something has changed in the Google code.
The status bar no longer displays 'go to website.com' when hovering over the ads.
It is suspected that this might have been a deliberate change on behalf of Google to kill click-tracking scripts. Why? For content and relevancy, which is ultimately Google's goal.
With the recent closing of the arbitrage accounts, Google has made a statement that publishers should concentrate on the content of their site, rather than on the performance of the ads. Disabeling third party click tracking is another sign they are moving in that direction.
Forum discussion continues at WebmasterWorld.