In addition to QuickTime 6.5 and new iTunes integration with AOL, Apple also quietly released iTunes 4.2. The new version includes changes required for the AOL integration, as well as what Apple refers ambiguously as "a number of performance improvements." From the release notes:
Whatis new in iTunes 4.2
iTunes 4.2 allows you to sign in and buy music from the iTunes Music Store using either your AOL or Apple Account, view the iTunes Music Store in a separate window, and includes a number of performance improvements.
The download weighs in at 9.8 MB, and can be found at Appleis iTunes download site.