Apple has been pretty selective about which of their young are able to benefit from Lion’s Internet Recovery feature, which allows users to reinstall the operating system over the network from Apple’s servers. It’s extremely helpful if you bork your install and don’t want to boot from a flash drive, and it will likely become the standard for repairing optical drive-less Macs as new models roll out.
About iMac EFI Update 1.7
This update enables Lion Recovery from an Internet connection and includes fixes that resolve issues with Apple Thunderbolt Display compatibility and Thunderbolt Target Disk Mode performance on iMac (early 2011) models.
Hit the source to download, or check Software Update on your machine.