Regarding the rumors for a 12" Retina MBA...
I'm all for retina standards as long as they don't decrease the actual screen real state of the current 13" MBA (1440x900).
If all they do is to take the current 11" MBA (1366x768) and double it to transform it into Retina, then I'm staying with my current 13" MBA. I value desktop real state over ultra-crispy resolution finess because, due to work, I require multiple applications loaded up at the same time.
This is just the same reason as of why I bought the 13" MBA over the 13" rMBP: the rMBP might be crispier but it fits less amount of stuff on the screen.
On retina macs there is a scaling option that will allow you to have more screen estate. It makes the ui elements proportionally smaller but they still appear crispier than on a non retina display of course.