I may be a bit slow on the uptake, but I've just discovered Mechanical Turk. It's a service offered by Amazon, described as "artificial artificial intelligence". Here's the blurb off their site:

Get results from Mechanical Turk Workers. Ask workers to complete HITs - Human Intelligence Tasks - and get results using Mechanical Turk...

As a Mechanical Turk Requester you:

  • Have access to a global, on-demand, 24 x 7 workforce
  • Get thousands of HITs completed in minutes
  • Pay only when you're satisfied with the results

My interpretation is that by paying them a small amount for each task assigned to them, Amazon have a huge pool of people at their disposal.

Could this be used for certain kinds of online usability testing? Has anybody tried using the service for that? I wonder how precisely you can specify which workers are assigned to your HITs?