Someone should implement a CAPTCHA system that simply presents the user with random HITS from Mechanical Turk (perhaps not all of them are suitable though) and collects the profit.
Note: Mechanical Turk has been originally created as a way for Amazon to provide their machine learning algorithms with labelled data; i.e. to train the AI.
It's a lot harder to take this stance if your site is impacted by the arms race, but it is cheery news for the technologist inside us all.
One caveat is that this sort of development seems more likely to remain in the darknet.