Amazon’s Mechanical Turk is one of many services that Amazon offers to developers. This one is a little more interesting then EC2 or S3, but in a very different way. EC2 and S3 allow you to buy Computing Power, but Mechanical Turk allows you to buy Man hours. Let me explain a bit.
You create a HIT (Human Intelligence Task) which asks a user to do something. something that a computer may be possible to do, but a human would be better at (say reviewing a document as assigning it keywords, as the example does). Each HIT has an allotted completion time, price, and some other bits a pieces. once you say the HIT is accepted, the person on the other end gets paid for completing their task.