When my MBP died I switched to a iMac 21.5 with an external monitor. It became so much easier to record Keynote presentations with the new setup. I recorded in slideshow mode fullscreen on the 21.5 while my current slide/next slide was on the external monitor.
If I get a MBA 11 then can do it the same way. If I go with a MBA 13, recording full screen becomes more complicated. I realize that this is not brain surgery and it's been figured out before. I want to simplify my workflow and it feels like going to a 16:10 screen takes me a step backward.