With threeothersoftware updates out the door today already, you could have forgiven Apple for not providing a fourth. However, Apple has also released an updated Firmware Restoration CD (version 1.6) for for a number of Mac models:
Xserve (Early 2008)
MacBook (13-inch Late 2007)
iMac (20-inch Mid 2007)
iMac (24-inch Mid 2007)
The Firmware Restoration CD is used to bring the firmware on an Intel-based Macintosh back to factory condition in case of an emergency (such as an interrupted firmware install). Apple makes a note that you cannot use this CD to restore the firmware that has already been successfully applied to your system; this is used only for systems that did not successfully get a firmware update applied.