The update brings with it improved reliability when booting your MAc system from a network.
As well as addressing an issue that can prevent HDCP authentication
after a reboot. Together with resolving an issue with boot device
selection when a USB storage device is hot-plugged.
Driect links to each update is listed here: Mac mini EFI Firmware Update 1.6 - Mac mini (Mid 2011), iMac EFI Firmware Update 1.9 - iMac (Early 2011), MacBook Air EFI Firmware Update 2.4 - MacBook Air (Mid 2011), MacBook Pro EFI Firmware Update 2.7 - MacBook Pro (Early 2011) and (Late 2011)