Earlier this month, Apple released a MacBook Air EFI update (version 2.9) with fixes for issues with the laptop waking from sleep. Approximately a week ago, the firmware update was removed by Apple because of bugs causing MacBook Airs to crash.
Today, Apple has re-released the update with fixes as version 2.9.1:
This update replaces EFI Firmware Update 2.9 and is recommended for MacBook Air (Mid 2011) models.
The update can be found for mid-2011 MacBook Air owners in the Software Update section of the Mac App Store.