Rory recently posted about two software developer types: 1) the kind that takes everything seriously and lacks a sense of humor or fun and 2) the kind that has fun while programming. I think he's right on, but I would say that this applies generally to almost any type of profession. I've seen and worked with musicians, manufacturing engineers, truck drivers, software developers, and retail clerks who all either take their job and lives way too seriously or try to have fun while doing good work. I don't think it only applies to developers.

There's also a sub-type of the "serious" developer: a person that takes things too seriously but if you asked them they'd say that they always have fun. Of course there are as many sub-types as there are personalities in the world.... but this one commonly appears. Feel free to list some others :)