Microsoft is making a selling point of the fact that the new Zune HD and associated software update are optimized for Windows 7, which is due out on October 22. I've got a copy of the final release code of Windows 7 on my work PC, and there is some useful synchronization between the two. For instance, the Quickplay menu in the Zune software--which lets you get immediately to music you've recently added, your Smart DJ stations, and any other favorites you want to "pin" to the list--is propagated into the Windows 7 Start menu. So even if you don't have the Zune software open, you can simply navigate to the Zune icon in the Start menu and all your Quickplay selections will show up.
Of course, Microsoft's had access to final Windows 7 code for a long time. But what about Apple? The company kindly sent me a new-model iPod Touch and Nano to test out, and I noticed that the boxes say they're compatible with Windows XP and Vista (and Mac OS X 10.4.11). Windows 7 isn't mentioned. I downloaded and installed iTunes 9 on my Windows 7 PC anyway, and I'm now happily syncing my music library. I haven't noticed any bugs or errors. (Your mileage may vary--this isn't a review, just my personal experience.) But this underscores my general impression of Windows 7 as a solid upgrade to Vista--not a fundamentally new OS, like Vista was to XP. As Microsoft has said, if your apps work with Vista, they'll almost surely work with 7.
The more interesting question is how did I get my music library onto my work computer in the first place? Simple--the Zune software has, from the very beginning, had a reverse-sync feature. You simply drag all the songs from the Zune icon to the PC icon, and they go happily traversing your USB cable down into your PC. iTunes has no such reverse-sync, and in fact is pretty strict about only allowing you to sync with one library at a time, although there are plenty of third-party apps that can do it for you.