I like to do coursera free courses, as I find ongoing learning fun and satisfying.
My course this weekend was talking about intrinsic and extrinsic motivators. One of the studies showed the effect of
rewarding a task that was innately satisfying with money for performance, and the effect that had on performance over time.
Initially there is a spike in performance of the rewarded compared to the unrewarded control group, but then for the sessions after, performance drops compared to the control group. As part of the experiment, after the 'monitored' time they were left alone and thought they were unmonitored. In the control group, people still generally performed the task as it was 'fun', but the group who'd been rewarded had a much lower rate of doing so. They weren't being paid, so why bother?
I think this has interesting repercussions for the 'be paid for what you love' movements. For example, that you may end up not loving it as much, or you won't doing it as much if the money is not coming in. It's important to note, though, that there seems to be a difference on whether the pay is for performance (successful completion of tasks), vs not being tied to performance.