Amazons Artificial Artificial Intelligence
People can register with amazon to perform so called HITs (human intelligence tasks) for a small fee and programmers can use the API supplied by amazon to query this group of people - for example to ask if there is a tiger in a picture.
This is really a cool and innovative idea, although I'm afraid it will end up causing even more SPAM ... A while ago I did some consulting for a firm building anti-spam software and one of the topics where "turing tests" (CAPTCHA) that for example stop spammers from creating free email accounts (you all know these pictures showing distorted numbers that you need to write into a form in order to prove that you are a human). Back then I learned about some porn / spammer joint ventures that where defeating these tests by enlisting the help of people looking for free porn: "write down the distorted number shown in the picture to get another page of free porn pictures", the pictures where taken just in time from the site of a free email service and the answers would be used to create a new account. I'm afraid amazons "mechanical turk" makes it easier for spammers to defeat this kind of test.