Originally Posted by
monroeski
They kind of do. Notch mentioned that biomes will appear in your current maps, but you actually have to travel beyond the borders of what you've already discovered (thus generating new land) to find them. In other words, you won't find them in any of the land that you've already discovered. You could extrapolate that to mean all the new stuff, though of course that's just an assumption, but what else would he do, just randomly change existing blocks into one of the 6 new types? Surely at least some of the new types are directly related to biomes.
I imagine other stuff, like the new enemy, can show up pretty much wherever they want, and nobody really knows anything about the portals to hell at this point.