Reader Brett writes in with an interesting observation about his shared iTunes library, which he plays from his laptop and his desktop:
Previous to the latest update of iTunes, I could only have one installation of Itunes running at a time, either the desktop would work or the laptop would work. The error message was something like iTunes library already in use.' However, with the latest release, I've found that I can have iTunes open on both.
A quick test between my MacBook and Powerbook confirmed Brett's findings. You can play music from a single shared library between two machines and edit ratings and playlists, which update on each computer—effectively removing the need to sync the iTunes library file manually. But it's not perfect. Listening to the two libraries at once, for the most part, goes without a hitch. Playcount and ratings do update across libraries (eventually, if not immediately.) If you edit ratings on a song (which means iTunes has to write to its library file) and try to access that same song right away, you'll get an error like this one:
So this isn't without its choppiness or risks. I also had one machine intermittently lose track of where media files were located on the shared drive while accessing the same library. (You get the little exclamation point and iTunes says it can't find the file, and prompts you to browse for it.) In both cases, by just restarting iTunes all was well again.
Disclaimer and notes: I only tested this on two Macs, not two PC's, using the Mac's built-in file sharing. As far as I know, the iTunes library file is not compatible between Mac and PC, so I doubt that will work at all. Brett says he had this working even when the library was shared remotely with Hamachi. If you try this yourself, be sure to back up your iTunes library first, because having two machines write to the same file can corrupt it. Anyone else give this a try? Let us know how it went in the comments. Thanks, Brett!