As recently reported on Slashdot, Apple, in its infinite wisdom, has added a checksum to the iPod database apparently to restrict non-iTunes products (like Amarok via libgpod) from having the ability to add music. To me this sounds pretty familiar. This is the same thing they did to iTunes 4.5 to make it harder for other apps to read off their DAAP shares, they changed it again in iTunes 7; open source apps are still unable to read iTunes 7 DAAP shares.
http://amarok.kde.org/blog/archives/496-iPod-Classic-Will-Be-Supported.html