For me I think the determining factor of a good programmer is not enjoyment (although that is necessary), it's curiosity. I work with a guy who I'm pretty sure has a photographic memory and would probably run circles around me in an IQ test and with his GPA, but I'm constantly showing him more efficient ways to write code. The difference is I am forever curious about CS-related stuff. I spend hours a day reading HN and other things like it. I'm orders an of magnitude better prgrammer than he is simply because I'm curious.