I've done the deed at last and have re-equipped with a nice 128gb macbook air 11. It turns out to be ideal for mobile development as it's reasonably fast and once I'd installed xcode, was a dream to use.
The screen resolution is great. I didn't realise that it was so much higher than the standard macbook 13.
So now the macbook pro is relegated to the desktop, where it's plugged into a 1920 * 1080 display and acts as my general flash dev machine. The air is now my road companion and my ios and android app dev machine.
If anyone is on the fence about these little beauties I would say get one if you want an ultra portable office. I now have my reference library on my ipad. I can carry both for pretty much the same weight as carrying just the 13 inch macbook pro!
My productivity has gone through the roof!