Elevator pitch: There's a missing gear in the machine of psychology research. Every significant human study requires weeks or months of data collection, and more time coding that data in a form that can be analyzed statistically. This makes it infeasible to do the sort of fast, iterative refinement of models that biology has seen in recent years.
Amazon's Mechanical Turk provides the missing piece. It provides an accessible interface for building a survey, interactive test, or other psychological measure, pushing it out to thousands of participants, quickly returning the results to the researcher in electronic form, and screening out unusable data. It's flexible enough to allow screening and debriefing, and gives access to a vastly larger pool of participants than Experimetrix. And it's cheap.
First, take a look at this: Ten Thousand Cents.
When I first heard about bioinformatics I was under the impression that it was the exponentially increasing power of computers that made it irresistible to start using them for biological research. But actually, it was pretty much the reverse -- high-throughput experimental methods like gene sequencing, mass spectrometry and X-ray crystallography generated too much data for humans to process manually. Computers were only barely able to handle this workload in 1986, when the human genome project started -- scientists just did what was needed to move around the mountains of data coming out of their experiments. Similarly, new computational research is coming out of the Large Hadron Collider project now.
Psychology researchers (especially in social psychology) currently spend semesters at a time gathering data for their studies and converting it into data that can be quantitatively analyzed. High-throughput experimental methods are scarce and expensive, so there's no "data glut" driving the development of better information-management methods. Progress in the field is slow and lossy -- since there's not much demand for the raw data, conclusions are described qualitatively, which makes it hard to use prior results as a solid foundation for future work.
With Mechanical Turk, it's possible to do in one shot a study that would otherwise require a meta-analysis of several studies across particular locations or demographics. With more consistent data and larger populations, data can be reusable.
How it could work
If it fits behind a web interface, or can be described and completed with plain language or pictures, it can be done with Mechanical Turk. Necessarily, a form of consent can precede the main task, and a blurb of debriefing can finish.
To get a feel for how it's done, read this article: The Faces of Mechanical Turk
Naturally, the first study done this way should be something to determine how the population of Turkers corresponds to the general population and the student populations that have already been characterized in previous studies. A public-domain measure of the Big Five or something like the Narcissistic Personality Inventory would be good candidates. Then, let slip the hounds of statistics. Are Turkers as representative of the general population as psychology undergrads? More so?
Some research along these lines has already been blogged here: Mechanical Turk Demographics
Now, let's try some examples.
Surveys: You craft a survey, Turkers take it, and you retrieve and filter the results through the Mechanical Turk interface. Pretty straightforward, no?
Coding visual or audio data: Following the original intent of Mechanical Turk more closely, this application of the service distributes a repetitive task normally performed over several weeks or months by the researcher or a group of grad students. Rather collect new data about a participant, this simply boils down a vast quantity of data that's already been generated -- this is a problem we want to have. A two-step example: (1) run a Mechanical Turk task in which participants draw or assemble an arbitrary image; (2) run a second task with a different set of participants who look at these images and code (type or select) the relevant traits they see in the images.
Measure development: One of the more uncomfortable questions in social psychology research is the validity of personality measures. Devise a series of questions and a method for tabulating the results; run it on some participants; analyze the results to get some answers. But, what's really being tested here -- the population, or the measure? Tragically, there's no time to refine the measure very much; if the results are useful, you run with it. But! With Mechanical Turk, collecting survey results is cheap and quick; and since the general format of the survey isn't changing between revisions, the same set of statistical transformations can be applied programatically to each iteration of the survey.
This is a great way to build a psychological measure that you can be confident in: Push an initial draft of the measure out to Turkers, receive some results, perform a statistical analysis and save the operations as an R or SPSS script. Then, manually refine the measure, put it back on Turk, filter the new results through your analysis script, and repeat until it looks good. This can get as advanced as you'd like -- start with several times as many questions as you'd like to see in the final survey, then automatically dispatch random subsets of the question list to Turk, filter through your automatic analysis to get some scores indicating quality, and use a Bayesian classifier to narrow down the best possible subset of questions.
Update: Here's a conference paper on the same topic.