The major one I can think of right now is using lifted financial information and Mechanical Turk to make new accounts and use it to juice SEO or FB fan pages.
There are some that have made amazing use of Mechanical Turk without actually getting caught - that is one vector I think the affiliate industry has greatly overlooked.
Can you give us some examples of who has done this and how they avoided getting caught on Mechanical Turk? I've had legitimate HITs removed for apparently violating policy recently, so in my experience AWS is fairly vigilant in looking out for HITs that attempt to juice SEO or promote.
I guess it could work if you abstracted it enough so that it's not apparent to the worker, but it wouldn't be trivial to execute. Using VAs on Odesk might work better.
There are some that have made amazing use of Mechanical Turk without actually getting caught - that is one vector I think the affiliate industry has greatly overlooked.