I've been working on a friend's iPod recently. The otherwise healthy iPod has started freezing every time you move songs to it. Choose a batch of 20 songs and 5 or 6 will transfer fine and seven will die. The real problem is that it is not just the iPod that freezes but the whole computer. The machine (running Mac OS X 10.4) will stop completely. A few processes are "stuck" but even attempting to shut-d. own or restart the computer don't work. The only solution is to power down the computer and restart it. After a restart the whole scenario plays out again.
After several tries with other iPods and the computer it seemed to be a problem with the specific iPod. A trip to Apple Care and back and they report the iPod is just fine. Upon transferring the next set of songs the familiar freeze was back. The iMac locked up completely. Had Apple Care missed something? Why did this computer that works with other iPods not work with this iPod.
Eventually I decided to reload the iTunes library to make sure there wasn't a problem with the library itself. After taking all the files out and re-importing them there was no difference. Could it be the cable? The cable had been used for a couple of years and had never really been taken anywhere or used in any other way. However, it occurred to me at that point that the "other iPods" that were working fine were all USB models. Plugging the ill-functioning iPod into the USB cable it performs flawlessly. Somewhere along the line one of two things has happened. Either there is a problem with the firewire cable, which I'm still skeptical about, or there is a problem with the OS on the iMac and how it recovers from firewire errors.
More time and testing will eventually tell. For now the solution is a USB-Dock cable for the iPod.