iTunes 9.2.1 provides a number of important bug fixes, including:
Disables older versions of some incompatible third-party plug-ins
Addresses minor issues with dragging and dropping items
Addresses a performance issue when first syncing to some devices with iTunes 9.2
Addresses an issue upgrading to iOS 4 on an iPhone or iPod touch with encrypted back-ups
Addresses other issues that improve stability and performance