Last I was on (which was a couple of years ago) you could get a good hourly rate (>$20/hr) if you knew how to sort the HITs properly. There were a lot of tasks where the payoff per task was very low, and if you believed their estimate of how much time it took per task the hourly rate was very low, but the task was actually much quicker than they estimated.

For example, a "which of these things is not like the other ones" type task might be estimated as taking 15 seconds, but if you're in the zone you can do them in 5 seconds, netting you 3x the hourly rate.