iTunes 4.0.1 update was released today via Software Update.
iTunes is the only software you'll ever need to build & manage your music collection on your Mac.
iTunes 4 features superior sound quality including support for MPEG-4 AAC audio. iTunes 4.0.1 includes a number of performance and network access enhancements, and only allows music sharing between computers using iTunes 4.0.1 or later on a local network (in the same subnet). If you have an Apple SuperDrive, you can archive your song files to a DVD disc as well as burn playlists to standard audio CDs to play in your car or home stereo.
Only allowing music sharing in a local network is likely a response to piracy hacks that allowed files to be copied over iTunes' current sharing method. Notably, this drew criticism and concerns from record companies.