I published an article in Dragon Magazine, and forever signed away all rights to it by so doing. Didn't really bother me much, but I'd hate to have to do that with my fiction. I suspect it wouldn't bother me as much if I was actually working in their worlds though, but even without all my world building being handed over to them to do with as they wish, just handing my characters over would be painful enough. shudder Tracy Hickman wasn't very happy with what happenned to Dragonlance after he created it, IIRC, and that was a major aspect of why he and Margaret went independant.