Do 64gb and 128gb SDXC cards work on the Macbook Air 2011?
It appears to work according to several reports:

http://www.zdnet.co.uk/reviews/ultraportables/2011/07/26/apple-macbook-air-2011-133in-40093522/


  There has been some concern that Apple lists the MacBook Pro models on
  its web site as having an SDXC card slot, for high-capacity SD cards,
  and only lists the card reader on the Air as an SD card one. We tried
  a 64GB SanDisk SDXC card in the MacBook Air's card reader, and the
  system recognised it as the appropriate size and was able to access
  files on it. However, if you're looking to get a massive SD card in
  order to augment the smallish 128GB SSD built into the Air, note that
  the card slot leaves the SD card hanging halfway out on the side of
  the system, so it's not appropriate for full-time use.


https://discussions.apple.com/thread/3014714?start=0&amp;tstart=0


  I got my Transcend SDXC 64GB flash card, and yes, it reads and writes
  perfectly in my MacBook Air.


According to iFixit it uses the Gensys logic GL822 SD slot controller which is a USB 2.0 high speed device (480mbps) and supports up to 2TB SDXC cards.