Lion Recovery
Apple’s sparse patch notes for the firmware update:
About iMac EFI Firmware Update 1.8
This update enables Lion Recovery from an Internet connection on iMac (Mid 2010) models.
For more information about Lion Recovery, please visit this website: http://www.apple.com/macosx/recovery/.
As of this writing, the firmware update isn’t showing up on Apple’s Downloads site, but if you have a Mid 2010 iMac, you should find it in Software Update as a 2.9MB download.