If this kind of click fraud is as widespread as the article makes it sound, then the Google and Yahoo ad models are going to run into problems:

PandaLabs has detected a network of computers infected with the bot Clickbot.A, which is being used to defraud ‘pay per click’ systems, registering clicks automatically and providing lucrative returns for the creators. According to the data collected so far, the scam is exploiting a global network comprising more than 34,000 zombie computers (those infected by the bot).

The bots are controlled remotely through several Web servers. This allows the perpetrators to define, for example, the web pages on which the adverts are hosted or the maximum number of clicks from any one IP address in order not to arouse suspicions. Similarly, the number of clicks from the bot can be monitored as well as the computers online at any one time. The system used can evade fraud detection systems by sending click requests from different, unrelated IP addresses.

I understand that Google, Yahoo (etc) look for this kind of thing, and have systems in place to detect it. It sounds like those systems aren't working as well as they would like though - and if advertisers start to realize that, the rates that can be charged will drop. Given that all the air in Google's stock comes from advertising revenue... well, I'm visualizing a paper bag, just before the hand comes in. There could be a real explosion.