This update supports general compatibility issues, and addresses overall stability and performance issues including the following:

Fixes an issue with the GarageBand Lesson Store not completing single or multiple lesson downloads.

• Corrects issues with some tempo-based effects falling out of sync with main song tempo. 
• Resolves problems with Magic GarageBand project files not opening up correctly in the GarageBand tracks view.

The update is recommended for all users of GarageBand '11.