I agree that World Builders Disease is a potential problem, and perhaps I expressed myself poorly in suggesting that one "build the world". I don't think that I meant to suggest building the world until it's "complete"; rather, I think, that world-building is a background activity, something done "behind the scenes", that shows through where relevant. I also think that it's very helpful to have at least some of the world-building done ahead of time — after all, how do you know what to imply if you don't know the relevant aspects of the world?
That said, it needn't be built to the finest detail: you may want to know ahead of time whether mages cast spells with arcane words, or weaving strands of reality, or summoning spirits, but you probably don't need to get into the fundamental metaphysics that governs sorcery unless that's part of what you're trying to convey.
Further, I have found that world-building can give rise to new story ideas: in some work of my own, discovering how a particular mode of transport worked — in general, at least — despite that detail not being terribly relevant to the piece in which it was mentioned, led me to further world-building ideas that in turn led me to a new story-plot.
I suppose that it's in part a matter of priorities: if writing the stories is given precedence over building the world, then World Builders Disease shouldn't be a great danger.
 We apparently don't have an article on World Builder's Disease, so I've de-potholed my references above. ^^;
edited 22nd Apr '13 9:12:40 AM by ArsThaumaturgis