I'm designing a grinder, and I'm wondering if the mob spawning algorithm has changed in the last few updates. For instance, in older versions mobs would spawn between 27-128 blocks from you or something. Is this still the same? Does it work vertically as well as horizontally? I'm just trying to exploit the algorithm as much as possible to build an awesome grinder.
He describes how the spawning for passive mobs has changed. It may effect how you build your spawner.