Yesterday, Apple gave Mac Pro owners an EFI Firmware update. Here's what Apple says about the update:
This update fixes several issues to improve the stability of Mac Pro (Early 2008) computers.
To complete the firmware update process, please follow the instructions in the updater application (/Applications/Utilities/Mac Pro EFI Firmware Update.app). The updater will launch automatically when the Installer closes.
To download the firmware updater, open Software update or download the installer package from Apple's support downloads website.