I understand that they are currently turned off because of issues with 1.3 Can we expect them to be turned back on at some point in the future?
Update. I see that mobs are alive and kicking in the Aether, however when I try to spawn chickens using eggs.. it does not work. I am trying to build a chicken farm and it does me no good to have friendly mobs available if they can't be spawned. Can someone update this post and explain if there is a setting that allows for spawning with eggs etc and if it will be turned back on?