Had some absolutely bizarre results from their attempt to integrate mturk with Bedrock's 'ground truth' thing as of a few months ago. Threw simple mnist digits recognition at it, see what the quality, timing, and cost was. Figured mnist digits was at this point trivial. Spent $10 and the accuracy was marginally better than guessing, completely unusable results. Was completely baffled, people were publishing peer reviewed research based on exclusively mturk results.
