For the people crossing over, what is your motivation?
For 11" owners, you get an inch more of screen, for the 13" owners you lose an inch.
Plus you give up on well established USB port in favor of the new USB-C.
I'm not knocking the decision or the MB, but rather, I'm interested in knowing why
I haven't committed to buy one, but I'll tell you why I might. Note that I'd be going from rMBP to rMB, not MBA to rMB.
Right now I'm carrying a 13" rMBP and an iPad (was an Air; got too big and heavy so changed to an rMini) every day. It's ok, but I notice the weight. And at work I don't need (actually
can't use) the USB ports for data exchange. The rMB should be able to handle the things I use the rMBP for at work and while commuting - mostly Word, Excel, Outlook and Safari.
So, getting rid of almost 1 1/2 pounds of laptop with no give-up in screen quality or connectivity is really no issue at all. The slightly smaller screen might or might not be an issue under some conditions, since I often need to have two documents open at once and the 13.3" screen might be just enough bigger to make a difference - hard to tell without trying it in person.
The biggest issue is whether I feel like putting $1300 into that dedicated use (and keep the rMBP), or justify the $1300 by selling the rMBP (not inclined to do so - and I do things with the rMBP at home, like photo and video editing, that I'm not sure the rMB is a good candidate for. A secondary issue is whether it's dumb to buy a Gen1 design. The original Air and iPad were innovative but not fully developed (duh). Resale value is probably high enough that I might take that risk.