Apple released GarageBand 4.1.2 today which is a minor update described as:
This update improves overall stability and addresses issues with the automation of software instrument parameters, FireWire and USB based audio devices and Magic GarageBand.
I had no problems installing the 19.9MB update through Software Update on my Intel Macs. But I don’t use GarageBand so I have no idea what affect, if any, it has. It’s also available as a 19.1MB standalone download. No reboot is required.