Although I am very pleased with my MacBook Air in general, there are two things I would very much like to see improved in the next generation.
When running on battery it only lasts half a day. I have a lot of apps running so the 7 hour battery life Apple claims is nowhere to be seen. By lunch I have to charge it and when the second part of the work day is over it's time to do it again. The iPad easily runs for 10 hours without having to be charged. I have gotten so used to it that I miss it when I'm on the Mac.
This is also something I blame on the iPad. The retina display is so crisp and even though my vision isn't perfect I experience the difference quite a lot.
If there was a MacBook Air with retina display and at least 8 hour battery life in real work conditions I would want it real bad.