I ran into this
interesting note from Caterina Fake (Flickr co-founder) in her blog. She's quoting Evolutionary psychologist Nigel Barber, who cites a study where kids were given pens to play with:
"Surprisingly, those who were rewarded for doing so were less inclined to continue. "The underlying explanation for psychologists is that when you pay somebody to do something ... they get the feeling that they're not doing it because they enjoy it," Barber said."
