Apple has posted an update for the hard drive of the iMac and the Mac Pro.

The Hard Drive Update 1.0 includes bug fixes and important updates for the following systems:
iMac Core 2 Duo (Mac OS X 10.4.7 or later)
Mac Pro (Mac OS X 10.4.7 or later)

Important:
It is strongly recommended that you back up the data on your hard drive(s) to an external drive or removable media before running this update. Do not reset, shut down, or turn off power to your computer while updating the firmware. If an error occurs during the update process, your hard drive(s) may become unusable. In that case, all data on the drive(s) may be lost.