assuming macbook airs are the future of apple's notebook lineup, i for one will be mourning the loss of:
-upgradeable ram: i don't think i've ever NOT upgraded the ram in a computer i've owned. its great from apple's perspective though... whenever you start hitting ram limitations, just buy a new computer!
-discrete graphics: i have a hard time even picture apple ditching this, considering improved graphics were one of the main selling points of the 2011 upgrades, but you never know...
-FW800: i know this is one of those niche requirements like optical drives, but for me it would TOTALLY kill usability in my working environment. maybe thunderbolt will have stepped up to the plate before my next upgrade cycle in a few years, but right now the ecosystem is still extremely scant. plus, are you forced to buy a thunderbolt display just to be able to daisy chain with hard drives? do you have to disconnect the display every time you want to swap drives?
-ethernet: this one is a bit of a toss up. i'd be ok with losing it if wifi weren't still such a finicky affair. i'm mostly wireless these days, but at work copying gigabytes of data is still better done wired.
whatever the case, i'm sorta happy i've got a 2011 machine to last me in case whatever comes out this year needs a revision or two to iron out these concerns...