Weiman said that one of the major obstacles to a click fraud crackdown is that search engines are reluctant to share the data that documents such fraud. She spoke of one instance in which her client had been billed for traffic that had apparently been generated fraudulently, and the search engine involved hadn't done anything to prevent it. "The search engine clearly wasn't being proactive in detecting fraud,"
Also via John, a "let's pile on GOOG" piece at Business Week. I'm surprised there's no mention of click fraud. But the "one-trick pony" line may be enough for a while... It's precisely because of the one-trick pony (i.e. 90%+ of revenue from AdWords) that Google is very susceptible to the click fraud meme.