The new Pros are effectively Airs in weight but not in battery. What about the 12inch MacBooks? Aren't they effectively Airs minus the ports (a dongle could solve that problem).
In my experience the 12inch Macbook is not an Air replacement. The CPU is super-slow, and the keyboard is very poor (maybe I just got a bad one I don’t know... but I find it almost useless).
I had one of those too, and ended up returning it. I have large hands and found the form factor very uncomfortable. The CPU is also slow and the keyboard sucks (particularly disliked the arrow key configuration).