Apple has updated GarageBand to version 4.1.1.
The release appears to be a maintenance patch, and ships in conjunction with new versions of QuickTime and QuickTime Broadcaster. The latter updates are designed to address widely-reported security problems in Apple's multimedia software.
GarageBand 4.1.1 is described as "improving overall stability and addressing issues with file export to iPhone." It's a 47.8MB download that's available now from Apple's Downloads website and also through the Software Update feature of Mac OS X.
Installation of the update requires Mac OS X 10.4.9 or later, and that iLife Support 8.1.1 be installed.