Apple today released Bluetooth Firmware Updater 1.2 via software Update which provides improvements in the update installation process and improved performance and reliability.
The Bluetooth Firmware Updater is for D-Link USB Adapters (revision B2 or later), and Apple internal Bluetooth modules on PowerBooks and PowerMacs. This firmware update will improve connectivity between the computer and the Apple Wireless Keyboard and Mouse. Use this updater for the modules specified above; this updater is unsupported with any other Bluetooth modules.
Important: Applying this firmware updater to a D-Link USB to Bluetooth adapter will make it incompatible with non-Macintosh systems.
More info and download link (1.3MB) here.