Apple has released MacBook Air EFI Firmware Update 2.1 to address issues with Thunderbolt performance and OS X Lion Recovery over the Internet on 2011-model MacBook Airs. According to Apple, the update is intended to "resolve issues with Apple Thunderbolt Display compatibility and Thunderbolt Target Disk Mode performance on MacBook Air (mid 2011) models."
The 3.99 MB update is fairly large as firmware updates go (they're usually less than a megabyte), and as with all firmware updates, Apple emphasizes that you must not interrupt your Mac's power during the update lest you risk turning it into a very attractive brick. The update requires OS X Lion, which is pre-installed on affected model MacBook Airs.
Apple MacBook Air 13-inch (early 2015)