Perspectives on Psychological Science has a short piece on using Amazon’s Mechanical Turk as a subject pool: “Amazon’s Mechanical Turk: A New Source for Inexpensive, Yet High-Quality, Data?”
As Google Scholar shows, Mechanical Turk is being used in lots of clever ways.
Mechanical Turk has been called a digital sweatshop. Here are two perspectives – an Economic Letters piece: “The condition of the Turking class: Are online employers fair and honest?” And, a piece calling for intervention: “Working the crowd: Employment and labor law in the crowdsourcing industry.”
I've done a lot of work with mturk. It's great for large-scale repetitive tasks, but expect to spend a fair amount of effort setting up and doing quality control. One of the really interesting things about the Google Scholar links is the number of different journals and fields using mturk for research.