If you share your iTunes libraries across your network (there are some good reasons to do this, being able to play your songs on another computer without having to copy everything over there for one) you’ll find that the recent update to iTunes that brings it up to release 7 will break this sharing.
If you share between computers the solution is to simply bring all the computers up to R7 and you’re fine.
However, I use an appliance called a Roku Soundbridge that allows me to stream my music to our living room stereo. They have to come up with a patch to allow the soundbridge to interact with the new iTunes version. From the company’s support page:
Attention iTunes Users!
With the release of iTunes 7.0 today (9/12/2006), Apple has changed some of the underlying technology that allows the SoundBridge to communicate directly with iTunes. We hope to have an iTunes 7.0- compatible release of the SoundBridge software soon; however, at this time all SoundBridges are incompatible with the music sharing feature of iTunes 7.0. We recommend that SoundBridge owners wait for a SoundBridge update before upgrade to iTunes 7.0. Users wishing to upgrade to iTunes 7.0 (or who have already upgraded) can install the free Firefly media server to share their libraries with the SoundBridge. Firefly is available here.