Apple released Thunderbolt Firmware Update v1.2, an update that, "provides stability fixes for Thunderbolt and Target Disk Mode." The update is for Macs equipped with Thunderbolt, Apple's next generation I/O interface.
The patch notes for the firmware update:
About Thunderbolt Firmware Update v1.2
This update provides stability fixes for Thunderbolt and Target Disk Mode.
When your computer restarts a gray screen will appear with a status bar to indicate the progress of the update.
Do not disturb or shut off the power on your computer during this update. Note: Your computer must be plugged into AC power for the update to install.
It's a 1.22MB download through Apple's support site. Users with eligible machines should also find it in Software Update/the Mac App Store.