What if it becomes just fashionable to do it?
I mean, just to make nonsensical clicks

First we went from pay-per-view to pay-per-click, maybe some future day we move on to pay-per-buy.

(Amazon Affiliates already does it: they don't give you a single cent if you display their banner 100,000, you will only get a commission for actual confirmed sales.)

I think it's an interesting question – it's like the extension of the click fraud problem, but the Google marketplace is big enough to quickly "discount" such a move. Google itself could counter the move as well.

More on my take here: [ http://gotads.blogspot.com/2005/02/misunderstanding-market-ness-of-google.html]