Apple has updated their Logic Pro and Logic Express applications to version 9.1.1, which improves the implementation of the 32-bit Audio Unit Bridge and enhanced compatibility with 64-bit audio unit plugins.
Unlike many other updates Apple provides, there are nicely detailed lists of all the features and bugs that were addressed by these updates. You can read about them here:
The updates so far have not shown any problems, and the improvements have been welcomed by Logic users.
If you have Logic Pro installed, you should see these updates available in Software Update, so be sure to run that from the Apple menu. Additionally, be sure to fully back up your system and audio projects in an easily restorable manner before installing this update.
If you would like to download a standalone installer, they can be found at the following locations:
Logic Pro 9.1.1 (191.87MB)
Logic Express 9.1.1 (138.79MB)
Both updates require OS X 10.5.7 or later when running in 32-bit mode, and OS X 10.6.2 or later when running in 64-bit mode.