Interesting. You would not think the MBA13 only being 1" wider and 1.4" deeper would make that much difference.
I have also taken the road from the 11" to 13". I rely on it heavily since I travel much. Mostly by train. I loved the 11" which always worked good for me.
I think the 16:9 screen looks much cool than the 16:10 13". However I always had low battery on my 11" and while it was not a big issue since I had the cable with me the 13" has much better battery.
Still havent decided because the 13" is a bit too big for a few tray tables. Many of them have a hole in them for a drink or something and the 11" could sit nicely beside it but the 13" often get caught in it on one side - making the bottom case possibly scratch against the surface below. Therefore I have to rotate the computer a few degrees so I don't sitt entirely in front of it.
In that way the 11" is much better but the 13" has other benefits. The larger screen makes it possible for me to use it more as a computer than a "emergency computer". I can easily work with indesign which was difficult on 11" making it less useable.
Having the extra pixels makes a little difference and I used to zoom in on the 11" which I do not do on the 13" as much since the pixel ratio is lower on the 13".
I love the format of the 11" and perhaps I will go back, but being able to watch a movie, and work, and look at the battery meter and see 6:20 hours left is very calming. On my old 11" it would say 1:50 or something, perhaps the 2012 model is better, didnt have time to try it before I switched to a 13".
The bigger touchpad also makes a world of difference.
So there are both good things and bad things about it. I have an iPad that I can use almost like an 11" MBA. It weighs half of a MBA 11" so I can use that when I want to travel light. Otherwise the 13" is a good travel companion, not necessary to plug in as often and a good screen, keyboard and speakers(better than 11").
I think if there will be a retina 13" macbook pro that the gap between that and an air will be very small.
The smaller the computer gets the more limited I seem to get, even if I like it. So I think the compromise is necessary. I can carry both the iPad and MBA 13" and it is still lighter than my current MBP 15".
Another thing(!), I love to watch TV-shows on the MBA when traveling. My favourite show is Frasier and it is not filmed in 16:9 (perhaps some of the last episodes) so the 16:10 format is a bit better since it doesnt put so much borders around the video, and if I cut it or change aspect ratio it won't change as much as on 16:9.