I've been spending a not inconsiderable amount of time on mturk.com lately.
I had heard of Amazon's Mechanical Turk quite a while back, but had never really bothered to check it out until recently. Basically, mturk allows humans to either request or work on what are known as Human Intelligence Tasks (HITs) for micropayments. Read more here. If you're based in the USA or India, you can actually cash out your earnings. For everyone else, your earnings get deposited into an account with Amazon which you can then use to purchase items on Amazon.
It's generally difficult to make serious money (i.e. more than minimum wage) on mturk, although it's not unheard of. For Requestors, who may range from corporations to graduate students, the quality of work that you can get back from Workers on mturk is also of uncertain quality. But mturk is still a useful resource; that's why it's been around for a while.
I've been working on and off on mturk for the past two weeks or so as a personal project and experiment, and while I never really got to the point of making serious money, it was substantial enough to score me a chunk of change. I made about USD100 over about 10 to 15 hours of work spread over two weeks...and my first shipment of Amazon swag courtesy of mturk is en route to Singapore as we speak via vpost. This is probably an unsustainable figure though, as I scored some high-paying HITs that don't come by too often (One paid me $15 for a 750 word article I cranked out in a little over an hour).
I think I could probably sustainably make about $10 to $20 a week turking. That may not seem like a lot, but it does add up. More importantly, it doesn't feel like work. I complete HITs while surfing on the Internet, waiting for videos on Youtube to load, or just because doing HITs is fun. For instance, I've been completing a set of audio transcriptions of interviews done for a documentary on Polaroid, and it's been interesting hearing artists and photographers talk about why they still use Polaroid despite the prevalence of digital photography.
I've done transcriptions of classroom lectures by Mormons (deathly boring, and for some reason, mturk is stuffed with them), interviews with venture capitalists, interviews with an American manager of an auto components plant in Mexico who talks about offshoring of the auto industry (obviously part of a research study or dissertation), and an interview with the maker of the just released video game Mafia II (probably part of an entertainment channel that wanted a transcription).
So I'm a little picky with my HITs, but that's because I don't do it just for the money. Turking can be fun too.
If you ARE interested in making money on mturk, then you would probably want a strategy that maximizes profits and minimizes the time spent. Lots of strategies that you can google for out on the web. But personally, I'm just happy to make a few dollars each day doing something that's mildly enjoyable and not having to spend any cash at all the next time I order something from Amazon.