Half the world, seems like..! We have it on our iPad. Our 7-yo grandson went nuts over it when he visited in April. I play off and on, depends on how much time I need to waste!
However, I don't like the "feature" in the newest release that wants to call home every time you load the game (for ads, or updates, who knows?) But I was waiting at the blood donation center today, and couldn't play AB because they don't have WIFI for donors, and I had forgotten the password to reup my 3G connection. So I had to settle for playing the Rio version, which doesn't want to be connected all the time.