I guess the iPhone 3.0 update and Safari 4.0.1 weren't enough for Apple. Along with the just released update to Safari, Apple has just tossed in one more Software Update:
Bluetooth Firmware Update
"This update provides bug fixes and better compatibility with the Apple Wireless Mighty Mouse and Apple Wireless Keyboard. It installs on all Macintosh systems with Bluetooth based on the Broadcom chipset."
This update is only applicable to certain hardware configurations (as noted above), so if you don't see it, you don't need it. After running, the Bluetooth Firmware update will provide you with an installation screen and require a reboot when it's done.
I wonder if Apple will throw us any other new surprises today.