I think creating obfus satisfies a basic creative urge we all have; more normal people perhaps satisfy this urge through art or music or even conventional computer programing. I also find creating obfus to be an excellent form of stress relief. My personal obfu style, perhaps driven by stress, is to try to be humorous bordering on the absurd. My main motivation is not to make people spend hours figuring out how an obfu works, but simply to make them smile.

See also Learning from Obfuscation and domm's YAPC talk.