The Stepforth blog notes that the IAB has finalized guidelines related to Click Fraud at:
http://www.stepforth.com/blog/click-fraud-guidelines-finalized.php

Here's the post:

Click Fraud Measurement Guidelines Finalized by IAB
May 12th, 2009

Today the Internet Advertising Bureau (IAB) released version 1.0 of the guidelines for measuring click fraud
(http://www.iab.net/media/file/click-measurement-guidelines2009.pdf).
The guidelines were created with the aid of Yahoo, Microsoft and Google in order to ensure that all major search engines would back the finalized guidelines. Here is a key snippet from the document’s Scope and Applicability section:

The recommendations established in these guidelines provide the detailed definition of a “click” and the standard by which clicks should be measured and counted, including the identification of invalid and/or fraudulent clicks. The guidelines are intended to cover on-line browser or browser-equivalent based Internet activity. Additionally, any emerging technology utilizing standard HTTP protocols will be covered by these guidelines.
I doubt these guidelines will do much to quell the current click fraud cases that are in dispute but at least it will provide a clearer picture for future cases by establishing what each search engine has agreed is click fraud.

This quote from A.R. Ammons on clarity frames the benefits of these guidelines well:

I must stress here the point that I appreciate clarity, order, meaning, structure, rationality: they are necessary to whatever provisional stability we have, and they can be the agents of gradual and successful change.