That's true too, but what I meant was more specifically for MMOs (and games that have the player move in similar ways) - any bits of fun in the game should be n

That's true too, but what I meant was more specifically for MMOs (and games that have the player move in similar ways) - any bits of fun in the game should be not more than a 30 second drive/walk/run from another one. Imagine, for instance, a map of Elwynn Forest (if you've played WoW) and construct a graph over it of all the quest-related things to do or see - none of them should be more than a 30 second run from the nearest neighbor. Whether this is actually the case is an implementation issue :)