My wife and I share two PowerBook G4s; one of them is about 2x the speed of the other, so whoever gets first pick uses that one. A problem comes when I want to synch my iPod Shuffle, and my wife is using the computer that it is linked to. Here is a fix so I can use it on both Macs. First, delete (or move) your music folder on the Mac that the iPod is not linked to. Next go to Network and find the the Mac that the iPod is linked to, and mount your home directory. Next, Command-Option drag your Music folder from the iPod Mac to the non-iPod Mac -- this makes an alias.
Now when you start up iTunes, you will see all your songs from the other Mac, and you can plug in your iPod shuffle without any problem. A little warning that iTunes will get very mad if it doesn't have access to the Mac where your itunes library is stored when you launch it. A better solution might involve making a copy and then using rsync to keep things synced, or to store (a small) music folder on your .Mac account.
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One more thing is that you can do the same with your pictures folder and iPhoto.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050519185551144