Great post, deep subject
I've been there.
Problem is now if you go from the 11" back to the iPad it's limitations may bother you now than before you started taking the 11" everywhere

That's my experience.
If you're using a device to watch video, surf, write short amounts of text you'll be okay, but if you type a lot, or surf websites that require flash to work, for example mls.com you'll see it's limitations fast.
Yet, I love my ipad, use it many times everyday, great gps, excellent for flipping through pages of pdf's, looking up data as I'm typing on my Air, battery is great....
But, for the iPad to replace my little 11" Air as a take everywhere device, no way. I tend to take both when I can, if not the 11" goes for sure.
I use a usb high speed internet stick so I can get instantly connected similar to the iPad.
I have the 13" MBA too, bought both 2011 models with the idea the 11" would be for travel, plane, car and the 13" MBA would be my home office computer where I spend most of my time.
To my surprise lately I've ended up using the 11" a LOT at home and office too. It's size works anywhere, anytime I love it. In my office I have two ACD's on my desk connected to my Mac Pro ... still I'm using my 11", works on desk, can recline back in chair, move around...
Actually most of today I've sat on my couch at home on holidays grumpy because we're busy with work ... I've replied to an insane amount of emails ALL on the 11" ... I have the 13" right beside me, I find the 11" better on my lap, can type in any position literally, lol ... 13" is bit more awkward, like a normal notebook, not as 'fun'.
Makes me wonder if I even need the 13" MBA ... I 'think' I do because in theory more screen real estate equals more productivity, less scrolling, longer battery, SD slot etc, I should need and use it more than the 11" but i don't.
In a way I'd like to try making the 11" my "main" computer, office, home, travel. I have an ACD at office and home, the idea would be the 'brains' of my system are in a small 11" package, and just plug it into externals where ever I'm working. I have my Mac Pro in office for heavy lifting, video edits, server, back up etc. Having the 11" for 99% of my hands on time sounds perfect in theory.
It's the 11" screen that holds me back ... I don't like to work from a desk often, therefore I'd be looking at an 11" screen 80% of the time. A 13" could be better, or would it?
That's the thing with Apple, they make a great desktop, need it buy it, and they make a great MBP, need it buy it, then the MacBook Air's get powerful, of course I need it and buy it too.
The 13" was 'wow' and the go to machine for portable use up until October 2010 ... and then the an 11" came out too! Have to buy that, it's better on a plane tray, in the car, fun to use on the lap, gotta get the 13" too so when I'm at home I have 2 inches more screen real estate, plus the iPad's come out and we buy those too .... suddenly so many gadgets and many people spend a lot of time trying to figure which one is 'best' ... I'm guilty of that, many Apple fans are!!
Just rambling here, it's not a brief topic, lol, hope it helped in some way? My conclusion is the 11" MacBook is the most 'alluring' to me, that's why its my choice every time I go to do work whether it's editing a vector design or replying to a hundred emails.... it's the 11" I'm drawn to every time.
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