Apple has released a few updates for the EFI firmware in various Mac models from early 2011, which include new features and address a couple of prominent problems on the new devices. Firstly, the update enables Lion Internet Recovery for some systems that have not had it enabled (such as the early 2011 iMac), while improving its reliability in systems that already had it enabled.
Additionally, the update addresses a number of problems with Thunderbolt, including the performance of Target Disk Mode and compatibility issues with Apple's Thunderbolt Display.
The updates require OS X 10.6.8 or later, and should be available for relevant systems via Software Update (in the Apple menu), but can also be downloaded from the following locations:
The updates will download the firmware installer which will provide you with onscreen instructions for how to install the firmware. Be sure you have the system plugged in to a reliable power source before updating, and do not shut off or otherwise disturb the system during its update. Faults during firmware updates can result in broken hardware that will not function properly. The update will require you to restart your system.
As always, be sure to fully back up your system using Time Machine or a system-cloning utility before installing this update.