Apple is nonspecific about the exact issues the update fixes, but mentions graphics performance and compatibility with USB devices:
About MacBook Air and MacBook Pro Update 2.0The update is available via Apple's support website or the Mac App Store.
This update includes graphics performance and reliability enhancements and improves compatibility with some USB devices.
This update is recommended for all Mac notebooks introduced in June 2012.
Installing the update also changes the build number of OS X 10.8.2 from 12C60 to 12C3006.