A fresh Bluetooth Firmware Updater 1.2 is available from Apple. It is for D-Link USB Adapters (revision B2 or later) and Apple's internal Bluetooth modules on PowerBooks and Power Macs.
The update: "Provides improvements in the update installation process and improved performance and reliability," according to Apple.
Apple says: "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."
The company also notes that "applying this firmware updater to a D-Link USB to Bluetooth adapter will make it incompatible with non-Macintosh systems".