All a store visit told me was that a 13" screen is smaller than a 15" screen. It's not that I don't think I can get used to it, but I was looking for some input, especially from people who have made the switch so I do appreciate all the responses. The store experience doesn't say much about portability; I never had a problem with carrying my 15" MBP. However, the MBA is a lot cheaper and the primary reason I'd pay for a 15" MBP over a 13" MBA is the screen size. The extra power does nothing for my particular needs, but I also don't want to buy a new machine and have it "feel" like it's less.
well, it's a thousand dollar difference between the two so unless you specifically want the pro, i personally wouldn't spend that kind of money for a 2-inch larger screen. you could always get an external monitor with the substantial amount of money you would save choosing air over 15" pro - especially retina.
i have been using 13" monitors for years without ever "feeling" like it was a downgrade from the far larger laptop screens of yesteryear... of course, i've never "downgraded" in terms of specs with subsequent computers either.
that being said, even going from the MBP to the current MBA should hopefully feel like a power upgrade for you as well, unless you do specific tasks that would preclude a non-air machine which it doesn't sound like is the case for you.
My wife on the other hand hates "small" computers. she wants a lot of real-estate. Her work provides her with computers (as does mine) and she has held out getting a new machine for the past 2 years because she is frustrated with the removal of the 17" option. i think she's nuts, and i'm sure the feeling is mutual when she sees me with my 11" "calculator"
we're both scientists....
so really it comes down to personal taste. i apologize if my previous post was a bit snarky, but really - i think you can learn a lot more than "is it bigger or not" from using it first hand.
i walked in wanting the 13"mba. sure that's what i was going to get. walked out wanting the 11" and strongly considering the 15" rMBP...i know, i'm all over the place. but i was shocked at how light the SSDs and lack of optical drives made the new retina machines.
i really do think it is essential to use them in person up front. especially when you're looking at a $2K+ purchase in the case of the 15" machines.
good luck